sars-cov-2 vaccines, where do we stand?
TRANSCRIPT
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Comptes Rendus
Biologies
Alain Fischer
SARS-CoV-2 vaccines, where do we stand?
Volume 344, issue 1 (2021), p. 43-55
<https://doi.org/10.5802/crbiol.35>
Part of the Special Issue: SARS-Cov2 and the many facets of the Covid19pandemic
Guest editor: Pascale Cossart (Institut Pasteur, France)
© Académie des sciences, Paris and the authors, 2021.Some rights reserved.
This article is licensed under theCreative Commons Attribution 4.0 International License.http://creativecommons.org/licenses/by/4.0/
Les Comptes Rendus. Biologies sont membres duCentre Mersenne pour lâĂ©dition scientifique ouverte
www.centre-mersenne.org
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Comptes RendusBiologies2021, 344, n 1, p. 43-55https://doi.org/10.5802/crbiol.35
SARS-Cov2 and the many facets of the Covid19 pandemic / Le SARS-Cov2 et les multiplesfacettes de la pandémie Covid19
SARS-CoV-2 vaccines, where do we stand?
Vaccins contre le SARS-CoV-2, oĂč en est-on ?
Alain Fischera, b, c
a Institut Imagine, Paris, France
b CollĂšge de France, Paris, France
c UnitĂ© dâImmunologie, HĂ©matologie et Rhumatologie PĂ©diatrique, HĂŽpital NeckerEnfants Malades, Assistance Publique-HĂŽpitaux de Paris, Paris, France
E-mail: [email protected]
Abstract. Vaccination against the SARS-CoV-2, the virus responsible for the Covid-19 pandemic, rep-resents a major infection control strategy in the absence of effective treatment of the disease todate. Unprecedented mobilization has led to the development of a large number of projects, someof which have already been in test in humans for several months. The first efficacy and safety dataare expected in the coming weeks. New vaccine technologies are being evaluated (RNA, replicatingor non-replicating viral vectors), further increasing the chances of success. The criteria for evaluatingvaccinesâdespite the exceptional speed of their developmentâmust remain rigorous enough to en-sure their acceptance by the population. Beyond their development, mass production and equitabledistribution raise many questions. Finally, vaccination can only be successfully implemented if healthprofessionals and the population are convinced of its validity, which implies particular attention tothe quality of the information given and the methods of communication.
RĂ©sumĂ©. La vaccination contre le SARS-CoV-2, virus responsable de la pandĂ©mie de Covid-19 reprĂ©-sente une stratĂ©gie majeure de contrĂŽle de lâinfection en lâabsence Ă ce jour de traitement efficace dela maladie. Une mobilisation sans prĂ©cĂ©dent a conduit au dĂ©veloppement de trĂšs nombreux projetsdont certains sont en test chez lâhomme depuis dĂ©jĂ quelques mois. Les premiĂšres donnĂ©es dâeffica-citĂ© et de sĂ©curitĂ© dâemploi sont attendues dans les prochaines semaines. De nouvelles technologiesde vaccin sont Ă©valuĂ©es (ARN, vecteurs viraux rĂ©plicatifs ou non), Ă©largissant dâautant les chances desuccĂšs. Les critĂšres dâĂ©valuation des vaccins â malgrĂ© la rapiditĂ© exceptionnelle de leurs dĂ©veloppe-ments â doivent garder la rigueur nĂ©cessaire Ă leur acceptation par la population. Au-delĂ de leurmise au point, la production massive et leur distribution Ă©quitable soulĂšvent de nombreuses ques-tions. Cette vaccination enfin, ne pourra ĂȘtre mise en Ćuvre avec succĂšs que si les professionnels desantĂ© et la population sont convaincus de son bien-fondĂ©, ce qui implique une attention particuliĂšreapportĂ©e Ă la qualitĂ© de lâinformation donnĂ©e et aux modalitĂ©s de communication.
Keywords. SARS-CoV2, Covid-19, Vaccine ARN, Messenger, Adenoviral vectors, Spike, Elinical trial.
Mots-clés. SARS-CoV2, Covid-19, Vaccin, Messager, Vecteurs adénoviraux, Spicule, Essai clinique.
Available online 12th January 2021
ISSN (electronic) : 1768-3238 https://comptes-rendus.academie-sciences.fr/biologies/
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44 Alain Fischer
On November 9, Pfizer and BioNTech announcedthat their CoV-2-SARS vaccine consisting of the virusâspicule messenger RNA conferred 90% protectionagainst the occurrence of Covid-19, based on interimresults from a Phase III clinical trial [1]. This an-nouncement, whose media impact for a time over-shadowed the presidential election of the new U.S.president and the state of the pandemic, illustratesthe exceptional nature of this race for a vaccine. It be-gan only 10 months ago when the sequence of thevirus was published. It becomes even more impor-tant when properly evaluated (see below) in the con-text of an uncontrolled pandemic that has causedmore than 1.3 million deaths worldwide to date,caused by a virus for which no effective medicationexists at this time, despite ongoing research. On No-vember 16, Moderna announced that its RNA vac-cine has a short-term efficacy of 94.5%, confirmingwith a second preparation the first results providedby Pfizer and BioNtech. In addition, Modernaâs vac-cine appears stable at +4 °C for 30 days, which willfacilitate its distribution and use.
1. The race for vaccines
There has been an exceptional mobilization of thescientific, industrial, political, governmental, inter-national and non-governmental worlds to try to ob-tain in record time one or more vaccines that wouldmake it possible to stop or at least slow down thispandemic. Typically, it takes at least 10 years to de-velop a vaccine (Figure) [2, 3]. Because of the manystages: from concept, through pre-clinical trials, ani-mal models, toxicology studies, and then phase I clin-ical trials evaluating tolerance and dose, to phase IIand III trials evaluating efficacy and safety of use,to production, licensing, and distribution, it is con-ceivable that the timeline will be similarly long. InCovid-19, the challenge was to produce a vaccine in12â18 months. How is this possible without dero-gating from the strict rules of evaluation of theseproducts? The development of new technologies (seebelow) that considerably accelerate vaccine produc-tion, combined with the overlapping time of the dif-ferent stages and a risk-taking approach by anticipat-ing vaccine production are at the origin of this at-tempt to reduce the delays. To some extent, the ex-perience of Ebola vaccine development has served asa model, both technically and logistically, but with
a consequent change in scale. The clinical phaseswere started very early and ânestedâ. The potentialindustrial risk was largely offset by the massive in-vestment by some governments to finance vaccinedevelopment and production. This is undoubtedlythe case in China and especially in the United States.The government set up the âWarp Speedâ operation,which has financed the development of 6 vaccinesto date for more than 8 billion dollars, with the ob-jective of obtaining vaccines for 300 million US citi-zens [4]. In addition, many states, as well as the Eu-ropean community, have placed pre-orders for vac-cines to allow their citizens rapid access to vaccineswhen available, while providing guarantees to thecompanies involved in this race. As a result, morethan 200 projects have been launched. Their stage ofdevelopment varies widely, but more than 40 are inclinical trials and 10 are in Phase III trials, the first ofwhich began in late July. This proliferation of vaccineprojects has benefited from technological advancesand the development of new vaccine formulations. Intotal, there are seven forms of vaccines, ranging fromtraditional to novel strategies.
2. The different types of vaccines (Figure 1)
âą A classical approach is the use of inactivatedviruses, from viruses produced in cell cul-ture, which is a well-known technology, usedin particular for the influenza vaccine. Theyrequire the use of an adjuvant. This approachis particularly implemented by Chinese in-dustries with preparations in phase III clin-ical evaluation [5].
âą Another classical approach is the prepara-tion of live attenuated vaccine by producingnon-pathogenic modified viruses. This is thetechnique used for measles vaccine, for ex-ample. The need for preclinical optimizationstudiesâparticularly to ensure the genomicstability of the virusâincreases the time re-quired for development.
âą An innovative technique is the use of mes-senger RNA from the virus spicule [6â8]. Itis the genetic information coding for theantigens that is provided. The choice of thespicule is linked to the fact that it is the vi-ral protein that binds to the cell receptor(ACE-2) and allows the entry of the virus.
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Alain Fischer 45
Figure 1. Development timing of vaccine.
The neutralizing antibodies detected in in-fected patients are mainly directed againstthe spicule. This RNA is placed in lipidicnanovesicles that allow its cellular incorpora-tion, translation into proteins and ultimatelyimmunization. This is the technique used bythe Pfizer laboratory associated with BioN-Tech as well as by the company Moderna.This technique allows a completely acellularproduction and is accelerated. However, itsinnovative nature requires particular atten-tion to its safety of use. Finally, these RNAsare fragile and vaccines must be stored atâ20 °C or â70 °C depending on the prepara-tions. However, Moderna has just announcedthat they can be stored at +4 °C for 30days. An improved strategy (new generation)would be the use of a self-replicating RNAthat would reduce the amount of RNA tobe injected; however, such vaccines must becarefully evaluated for possible risks of notcontrolling this amplification in vivo [9].
âą The vaccine may consist of DNA coding forthe spicule in the form of plasmids. Again,mass production is relatively easy, but im-munogenicity appears to be lower and injec-tion modalities more complex [10].
âą Another solution is the use of viral vec-tors in which the genetic informationâthespicule geneâhas been added. Viral vec-tors incapable of replication are the sub-ject of major research efforts in vaccination.These are essentially adenoviruses, eithernaturally infecting primates or humans, butare of low prevalence to avoid the possible
neutralizing effect of pre-immunizationagainst the vector. Several candidate vac-cines of this type are in clinical evaluation(phase III) after obtaining rather positivepreclinical results [11â13].
âą A related strategy is the use of replicative vec-tors based on vesicular stomatitis virus [14]or the attenuated measles virus used forvaccination against this virus, in which theSARS-CoV-2 spicule gene is placed. Thesevaccines are in early clinical testing.
âą Finally, an attractive strategy consists in theuse of recombinant spicule protein producedin cell lines and associated with a lipid adju-vant [15, 16]. This vaccine can take the formof pseudo viral particles, an effective strategyin the context of vaccination against hepati-tis B virus. Modifications have been made tothe protein to stabilize it in its a priori mostimmunogenic trimeric form. Various prepa-rations are currently under clinical evalua-tion. Novavaxâs product induces a high titerof neutralizing antibodies in vaccine subjectsin Phase I trials [2].
3. Outstanding issues
It is very difficult to predict which strategy(s) will ul-timately be the most efficient. We can only be de-lighted with the diversity of approaches which ofcourse increases the chances of success. At this stage,it is known that several of these vaccines induce inhumans the production of antibodies neutralizing
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the viral infection as measured in vitro, at titres ap-parently comparable to those of the sera of conva-lescent subjects of Covid-19 [2, 3, 17]. They also in-duce at least a CD4 T response of the Tfh (follicularhelper) type required for antibody production, and ofthe TH1 but not TH2 type, which could contribute tobetter protection over time and avoid deleterious ef-fects of TH2 type responses (anaphylaxis, inflamma-tion) [18].
It should be noted, however, that no correspon-dence could yet be established between possibleclinical efficacy and neutralizing antibody titer (or T-response function). The kinetics of decrease in an-tibody titers are also unknown. Will it be similar tothat in infected subjects (rather slow in sick subjects,rapid in asymptomatically infected subjects)? [19].
The strategies developed so far are based on intra-muscular injections of vaccines, which are thereforeunlikely to induce mucosal immunity, although theirimportance in immunity against respiratory virusesis well known [20]. Some types of preparation couldbe used by inhalation, and this will probably be thesubject of further studies in the future. Finally, al-most all vaccines in preparation (apart from wholeviruses) use as antigens the spicule, the protein of thevirus that allows it to bind to its cellular ACE-2 recep-tor. This approach is logical because the neutraliz-ing antibodies found in infected patients are directedagainst this protein and in particular (but not exclu-sively) against the receptor-binding domain. The useof complementary antigens as a source of a protec-tive immune response cannot be ruled out. This canbe examined in a second step.
4. Criteria for success
Widespread use of an SARS-CoV-2 vaccine requiresthat it meets a set of efficacy and safety criteria thatcannot be deviated from despite potential pressures.The World Health Organization, the United StatesAcademy of Sciences [21] and especially the regula-tory authorities that issue the authorizations for use:FDA (food and drug administration in the UnitedStates), EMA in Europe have issued very precise rec-ommendations. Many points need to be considered:in addition to the quality of the vaccine product, firstand foremost are safety issues: is the immediate reac-tion (âreactogenicityâ) tolerable and what is the riskof serious adverse events? There is the question of
an aggravation of the disease by the effect of non-neutralizing antibodies which could either facilitatethe infection of macrophages or facilitate an exacer-bated inflammatory response. TH2 type T lympho-cytes could also contribute to this. This risk is notonly theoretical since it has been observed in sec-ond infection with dengue virus (arbovirosis) and inthe testing of a dengue vaccine [18] and experimen-tally with vaccine preparations against other coron-aviruses. However, a number of factors suggest thatthis risk is low in the context of CoV-2-CoV-SARS.Animal vaccination data are also other encourag-ing, but safety in phase III trials remains to be ob-served in this and other events. Careful monitor-ing will need to be maintained afterwards, particu-larly given the highly innovative nature of some ofthe vaccines. It is essential to be able to reassurethe public about the safety of these vaccinesâputin perspective with the expected benefitsâand tobe able to provide the public with the informationthey need.
Efficiency is of course central. But behind thisterm there are several notions: protection againstthe benign form of the disease, severe forms (muchrarer), duration of protection, effectiveness of protec-tion for vulnerable people, particularly the elderly. Fi-nally, are these vaccines capable of suppressing (orat least reducing the transmission of the virus) bypreventing viral replication in the oropharynx? Theanswer to these questions and especially the lastone will take time. The first so-called emergency ap-provals will depend on the rate of efficacy obtained,a trend towards the reduction of severe infectionsand a minimum delay in observation (2 months ac-cording to the FDA). Compaction of the develop-ment time for these vaccines should not lead to areduction in the safety and efficacy criteria. It isonly at this price that confidence in the vaccine canbe established. Note that the predicted efficacy ofPfizer and Moderna vaccines is observed in the earlypost-vaccination phase, at the peak of the immuneresponseâwhat will it be in a few months? The abil-ity of the vaccines to interrupt (reduce) the chance ofvirus transmission will depend on the ability to breakthe pandemic via herd immunity. If the vaccine wasperfectly effective [2], 70% of the population wouldneed to be vaccinated! There is also the possible needfor regular revaccination depending on the durationof protective immunity achieved.
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5. Who to vaccinate?
Vaccination priorities will be defined according tovaccine performance. The French High Authority forHealth is working in particular on this issue.
Professionally or socially exposed people (health,commerce, education, police, prison, people in pre-carious situations, etc.) appear to be a priority. Ifthere are indications of effectiveness among the el-derly and vulnerable, they should be vaccinated as afirst-line priority. Only then can the vaccine(s) be of-fered to the rest of the population.
6. Producing and distributing vaccines
Vaccine needs will be very large, ideally 15 billiondoses to vaccinate the entire world, taking into ac-count that 2 doses will be needed for most vaccines.Although production capacity is increasing, it is esti-mated that by 2021 it will reach four billion doses. . .This raises the question of vaccine distribution interms of both technical and ethical aspects. Technicalbecause some vaccines require storage at â20 °C orâ80 °C, which poses serious logistical problems. Howvaccine distribution will be organized, each countrymust prepare for this.
Rich countries have anticipated the acquisitionof vaccines for their citizens through pre-purchases:800 million doses for the United States, 5 doses perinhabitant for Great Britain, 400,000 million dosesfor the European community. . . Does this mean thatwe are moving towards a form of vaccine national-ism that is certainly understandable but problem-atic? [22, 23]. Indeed, effective control of the pan-demic implies vaccinating at least 70â80% of all theinhabitants of the planet. In this case, efficiency andethics combine to work towards this goal. How canwe ensure that these vaccines become a public good?The WHO proposes to initially vaccinate 20% of thecitizens of all countries, but we could go further andconsider, for example, vaccinating first in the coun-tries where the pandemic is strongest? [24]. At theinitiative of the WHO, CEPI (coalition for epidemicpreparedness innovation), GAVI (global vaccine al-liance), Covax was created, of which France and theEuropean community were partners from the out-set. The aim of this structure is to raise the neces-sary funds to make access to vaccines available inall countries of the world, including 50% of low- and
middle-income countries. The initial objective is toacquire 2 billion doses of vaccines. Will this initia-tive be sufficient to provide fair access to vaccines?It is too early to say, at this point in time the nec-essary funds have not been raised. However, com-plementary vaccine production initiatives, particu-larly in India, could help to ensure greater sharing.We would like to see a system of regulation and in-ternational governance capable of imposing such apolicy as well as regulation of vaccine prices. A formof political reconstruction of the WHO would in thissense be necessary, taking advantage of the Covid-19crisis [25â27].
7. Confidence in vaccination
A final key dimension of immunization success isconfidence in immunization. It is known to what ex-tent in France, but also in the United States, a reluc-tance to vaccinate has developed among a fractionof the population and health care personnel [28, 29].Recent opinion surveys in the framework of Covid-19have shown this again. It is therefore crucial that theimplementation of a vaccination program includesa series of measures aimed at building the confi-dence of both health workers and citizens. This in-volves, on the one hand, practical facilitation of vac-cination: simplified itinerary, vaccination by doctors,pharmacists and nurses, creation of mobile vaccina-tion centers, full coverage of the cost by the NationalHealth Insurance Fund, and on the other hand, tar-geted information campaigns with clear and trans-parent content [30]. Civil society through numerousassociations involved in public health issues must bemobilized in the definition of this policy and as amedia relay for explanation. Could be put forward ifone or more vaccines prevent viral transmission thefact that vaccination is the object of an altruistic atti-tude: vaccination of some protects the most vulner-able. The human and social sciences must be mobi-lized to specify these modes of action and evaluatetheir impact [31]. Demonstrating efficacy will posean ethical dilemma: the vaccine should be offeredto the control group at the cost of preventing fur-ther evaluation, which would be unreasonable [32].How can new therapeutic trials be considered in thissituation?
Several strategies could be considered [33]. Fi-nally, modeling tools should make it possible to
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Table 1. Main vaccines in evaluation
Principle Adjuvant Society Development stage Methods previouslyused for vaccines
âą Inactivated virus Alu. salt Sinovac Phase III Yes/multiple
Alu. salt Sinopharm Phase III
âą Attenuated live virus â Codagenix SĂ©rum In-stitute of India
Preclinical Yes/multiple
âą ARNm spike lipidicnanoparticles
PfizerâBioNTech Phase IIIâpreliminary results No
â Moderna Phase IIIâpreliminary results
Curevac Phase III
RNA auto replicative Curevac Preclinical
âą DNA plasmid â Inovio/Genexine Phase I/II No
âą Non replicativeadenoviral vectorChimp Ad Astra Zeneca/Oxford Phase III Yes Ebola
Ad 26 Johnson and Johnson/Janssen Phase III No
Ad 5 Cansino Phase III No
gorilla Ad Reithera Phase I No
Ad 5+26 Gamaleya Phase III
âą Recombinant spiculenanoparticules
Matrix-M Novavax Phase III (beginning) Yes
AS03 Sanofi Phase I
Virus-like particle Medicago Phase I Yes; hépatite B
âą Replicative vector
VSV-spike MSD Phase I No
Rougeole-spike â MSD-ThemisâInstitut Pasteur Phase I
Grippe-spike â Beijing Wantai Phase I
Alu: Aluminium; ad: adenovirus; vsv: vesicular stomatitis virus.
evaluate the effect of the vaccine(s) on the pandemicaccording to their efficacy and acceptability [34, 35].
The introduction of vaccination against SARS-CoV-2 is a vital public health, societal and economicaction. It cannot fail. Once it has been unequivo-cally demonstrated that one or more vaccines havea favorable risk/benefit balance, every effort shouldbe made to progressively program the vaccination ofpopulations on an international scale. Speed shouldnot be confused with haste, and the ability to resist
special interests, but it is a question of global mobi-lization to implement a common policy in the ser-vice of public health in order to achieve the progres-sive control of the pandemic. It will be essential tocarry out longitudinal studies of vaccinated subjects(so-called phase 4 study) to assess the efficacy (andsafety over time) according to groups (high risk, etc.).This evaluation will serve as a basis for forecastingthe need for revaccination and the evolution of thepandemic [35].
French version
Le 9 novembre dernier, les sociĂ©tĂ©s Pfizer et BioN-Tech annoncent que leur vaccin anti SARS-CoV-2constituĂ© de lâARN messager de la spicule du virusconfĂ©rait une protection de 90% contre la survenue
du Covid-19, Ă partir de rĂ©sultats intermĂ©diaires dâunessai clinique de phase III [1]. Cette annonce dontlâeffet mĂ©diatique a un temps Ă©clipsĂ© lâĂ©lection prĂ©-sidentielle du nouveau prĂ©sident amĂ©ricain et lâĂ©tat
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Alain Fischer 49
de la pandĂ©mie illustre le caractĂšre exceptionnel decette course au vaccin. Celle-ci a dĂ©butĂ© il y a seule-ment 10 mois lorsque la sĂ©quence du virus fut pu-bliĂ©e. Elle prend toute son importance, une fois cor-rectement Ă©valuĂ©e (voir ci-dessous) dans le contextedâune pandĂ©mie non maĂźtrisĂ©e responsable Ă ce jourde plus de 1,3 million de dĂ©cĂšs dans le monde, pan-dĂ©mie provoquĂ©e par un virus contre lequel il nâexistepour lâinstant pas de mĂ©dicament rĂ©ellement efficacemalgrĂ© les recherches en cours. Le 16 novembre, laSociĂ©tĂ© Moderna annonce Ă son tour que son vac-cin Ă ARN a une efficacitĂ© Ă court terme de 94,5%confirmant ainsi avec une seconde prĂ©paration lespremiers rĂ©sultats apportĂ©s par les sociĂ©tĂ©s Pfizer etBioNtech. De plus, le vaccin Moderna paraĂźt stable Ă +4 °C pendant 30 jours ce qui en facilitera la distribu-tion et lâutilisation.
1. La course aux vaccins
On a observĂ© une mobilisation exceptionnelle desmondes scientifique, industriel, politique, dâorga-nisations gouvernementales, internationales et nongouvernementales pour essayer dâobtenir dans undĂ©lai record un ou plusieurs vaccins qui permet-traient dâenrayer ou du moins de ralentir cette pan-dĂ©mie. Classiquement, le dĂ©lai nĂ©cessaire Ă lâĂ©labo-ration dâun vaccin est dâau moins 10 ans (Figure) [2,3]. En raison des nombreuses Ă©tapes : du concept,aux essais prĂ©-cliniques, des modĂšles animaux auxĂ©tudes toxicologiques, puis aux essais cliniques dephase I qui Ă©valuent la tolĂ©rance et la dose Ă ceuxde phase II et III qui Ă©valuent efficacitĂ© et la sĂ©curitĂ©dâemploi, aux Ă©tapes de production, dâautorisation etde distribution, on conçoit que les dĂ©lais soient aussilongs. Dans le cadre du Covid-19, le pari fut dâabou-tir Ă un vaccin en 12â18 mois. Comment cela est-ilenvisageable sans dĂ©roger aux rĂšgles strictes dâĂ©va-luation de ces produits ? Le dĂ©veloppement de nou-velles technologies (voir ci-dessous) qui accĂ©lĂšrentconsidĂ©rablement la production de vaccins, associĂ©aux chevauchements dans le temps des diffĂ©rentesĂ©tapes et une prise de risque par lâanticipation de laproduction des vaccins sont Ă lâorigine de cette ten-tative de diminution des dĂ©lais. Dans une certainemesure, lâexpĂ©rience de la mise au point de vaccinscontre le virus Ebola a servi de modĂšle, tant sur unplan technique que logistique mais avec un chan-gement dâĂ©chelle consĂ©quent. Les phases cliniques
ont Ă©tĂ© dĂ©butĂ©es trĂšs prĂ©cocement et âemboitĂ©esâ.LâĂ©ventuelle prise de risque industrielle a Ă©tĂ© trĂšs lar-gement amortie par lâinvestissement massif de cer-tains gouvernements pour financer le dĂ©veloppe-ment et la production de vaccins. Câest sans doutele cas de la Chine et surtout des Ătats-Unis. Le gou-vernement a mis en place lâopĂ©ration âWarp Spee-dâ qui a financĂ© pour plus de 8 milliards le dĂ©velop-pement de 6 vaccins Ă ce jour avec comme objectiflâobtention de vaccins pour 300 millions de citoyensdes Ătats-Unis [4]. Par ailleurs, de nombreux Ă©tatsainsi que la communautĂ© europĂ©enne, ont passĂ© desprĂ©commandes de vaccins afin de permettre Ă leursconcitoyens un accĂšs rapide aux vaccins lorsque dis-ponibles tout en apportant des garanties aux entre-prises engagĂ©es dans cette course. Ainsi plus de 200projets ont vu le jour. Leur stade de dĂ©veloppementest trĂšs variable mais plus de 40 sont en essai cliniqueet 10 en essai de phase III, le premier ayant dĂ©butĂ© finjuillet. Ce foisonnement de projets vaccinaux a bĂ©-nĂ©ficiĂ© dâavancĂ©es technologiques et lâĂ©laboration denouvelles prĂ©parations vaccinales. Au total, des stra-tĂ©gies classiques aux stratĂ©gies nouvelles, on compte7 formes de vaccins.
2. Les différents types de vaccins (Figure 1)
âą Une approche classique consiste en lâutilisa-tion de virus inactivĂ©s, Ă partir de virus pro-duits en culture cellulaire, câest une techno-logie bien connue, utilisĂ©e notamment pourle vaccin contre la grippe. Ils nĂ©cessitentlâemploi dâun adjuvant. Cette approche estparticuliĂšrement mise en Ćuvre par des in-dustries chinoises avec des prĂ©parations enĂ©valuation clinique de phase III [5].
âą Une autre voie classique consiste en la prĂ©-paration de vaccin vivant attĂ©nuĂ© en pro-duisant des virus modifiĂ©s non pathogĂšnes.Câest par exemple la technique retenue pourle vaccin dirigĂ© contre le virus de la rougeole.La nĂ©cessitĂ© dâĂ©tudes dâoptimisation prĂ©cli-nique â pour sâassurer notamment de la sta-bilitĂ© gĂ©nomique du virus â allonge le tempsde mise au point.
âą Une technique innovante consiste en lâutili-sation de lâARN messager de la spicule du vi-rus [6â8]. Câest lâinformation gĂ©nĂ©tique co-dant pour les antigĂšnes qui est apportĂ©e.
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8 Alain Fischer
Figure 1.
Le choix de la spicule est liĂ© au fait quâil sâagitde la protĂ©ine virale qui se fixe au rĂ©cepteurcellulaire (ACE-2) et permet lâentrĂ©e du vi-rus. Les anticorps neutralisants dĂ©tectĂ©s chezles patients infectĂ©s sont principalement di-rigĂ©s contre la spicule. Cet ARN est placĂ©dans des nanovĂ©sicules lipidiques qui per-mettent son incorporation cellulaire, sa tra-duction en protĂ©ines et in fine lâimmunisa-tion. Câest la technique utilisĂ©e par le labora-toire Pfizer associĂ© Ă BioNTech ainsi que parla sociĂ©tĂ© Moderna. Cette technique permetune production complĂštement acellulaire etaccĂ©lĂ©rĂ©e. Son caractĂšre novateur impose parcontre une attention particuliĂšre sur sa sĂ©cu-ritĂ© dâemploi. Enfin ces ARN sont fragiles etles vaccins doivent ĂȘtre conservĂ©s Ă â20 °Cou â70 °C en fonction des prĂ©parations. Tou-tefois Moderna vient dâannoncer une conser-vation possible Ă +4 °C pendant 30 jours.Une stratĂ©gie amĂ©liorĂ©e (nouvelle gĂ©nĂ©ra-tion) consisterait en lâemploi dâun ARN autorĂ©plicatif qui permettrait de rĂ©duire la quan-titĂ© dâARN Ă injecter ; nĂ©anmoins de tels vac-cins doivent ĂȘtre Ă©valuĂ©s avec prĂ©cautionquand aux risques Ă©ventuels de non-contrĂŽlede cette amplification in vivo [9].
âą Le vaccin peut consister en de lâADN codantpour la spicule, sous forme de plasmides. Ănouveau la production massive est relative-ment aisĂ©e mais lâimmunogĂ©nicitĂ© apparaĂźt
plus faible et les modalitĂ©s dâinjection pluscomplexes [10].
âą Une autre solution consiste en lâemploi devecteurs viraux au sein desquels lâinforma-tion gĂ©nĂ©tique â le gĂšne de la spicule â a Ă©tĂ©ajoutĂ©e. Des vecteurs viraux incapables derĂ©plication font lâobjet dâimportants effortsde recherche en vaccination. Il sâagit essen-tiellement dâadĂ©novirus, soit infectant natu-rellement des primates soit lâhomme maisfaiblement prĂ©valent pour Ă©viter lâeffet Ă©ven-tuel neutralisant dâune prĂ© immunisationcontre le vecteur. Plusieurs candidats vac-cins de ce type sont en Ă©valuation clinique(phase III) aprĂšs lâobtention de rĂ©sultats prĂ©-cliniques plutĂŽt positifs [11â13].
âą Une stratĂ©gie proche consiste en lâemploi devecteurs rĂ©plicatifs fondĂ©s sur le virus de lastomatite vĂ©siculaire [14] ou le virus attĂ©-nuĂ© de la rougeole utilisĂ© pour la vaccinationcontre ce virus, vecteurs au sein desquels estplacĂ© le gĂšne de la spicule du SARS-CoV-2.Ces vaccins sont en dĂ©but de test clinique.
âą Enfin une stratĂ©gie attractive consiste enlâemploi de la protĂ©ine spicule recombinanteproduite en lignĂ©es cellulaires et associĂ©eĂ un adjuvant lipidique [15, 16]. Ce vaccinpeut prendre la forme de pseudo particulesvirales, stratĂ©gie efficace dans le cadre dela vaccination contre le virus de lâhĂ©patiteB. Des modifications ont Ă©tĂ© apportĂ©es Ă la
C. R. Biologies, 0000, 1, n 0, 000-000
Figure 1. SchĂ©mas de dĂ©veloppement dâun vaccin.
Le choix de la spicule est liĂ© au fait quâil sâagitde la protĂ©ine virale qui se fixe au rĂ©cepteurcellulaire (ACE-2) et permet lâentrĂ©e du vi-rus. Les anticorps neutralisants dĂ©tectĂ©s chezles patients infectĂ©s sont principalement di-rigĂ©s contre la spicule. Cet ARN est placĂ©dans des nanovĂ©sicules lipidiques qui per-mettent son incorporation cellulaire, sa tra-duction en protĂ©ines et in fine lâimmunisa-tion. Câest la technique utilisĂ©e par le labora-toire Pfizer associĂ© Ă BioNTech ainsi que parla sociĂ©tĂ© Moderna. Cette technique permetune production complĂštement acellulaire etaccĂ©lĂ©rĂ©e. Son caractĂšre novateur impose parcontre une attention particuliĂšre sur sa sĂ©cu-ritĂ© dâemploi. Enfin ces ARN sont fragiles etles vaccins doivent ĂȘtre conservĂ©s Ă â20 °Cou â70 °C en fonction des prĂ©parations. Tou-tefois Moderna vient dâannoncer une conser-vation possible Ă +4 °C pendant 30 jours.Une stratĂ©gie amĂ©liorĂ©e (nouvelle gĂ©nĂ©ra-tion) consisterait en lâemploi dâun ARN autorĂ©plicatif qui permettrait de rĂ©duire la quan-titĂ© dâARN Ă injecter ; nĂ©anmoins de tels vac-cins doivent ĂȘtre Ă©valuĂ©s avec prĂ©cautionquand aux risques Ă©ventuels de non-contrĂŽlede cette amplification in vivo [9].
âą Le vaccin peut consister en de lâADN codantpour la spicule, sous forme de plasmides. Ănouveau la production massive est relative-ment aisĂ©e mais lâimmunogĂ©nicitĂ© apparaĂźtplus faible et les modalitĂ©s dâinjection pluscomplexes [10].
âą Une autre solution consiste en lâemploi devecteurs viraux au sein desquels lâinforma-tion gĂ©nĂ©tique â le gĂšne de la spicule â a Ă©tĂ©ajoutĂ©e. Des vecteurs viraux incapables derĂ©plication font lâobjet dâimportants effortsde recherche en vaccination. Il sâagit essen-tiellement dâadĂ©novirus, soit infectant natu-rellement des primates soit lâhomme maisfaiblement prĂ©valent pour Ă©viter lâeffet Ă©ven-tuel neutralisant dâune prĂ© immunisationcontre le vecteur. Plusieurs candidats vac-cins de ce type sont en Ă©valuation clinique(phase III) aprĂšs lâobtention de rĂ©sultats prĂ©-cliniques plutĂŽt positifs [11â13].
âą Une stratĂ©gie proche consiste en lâemploi devecteurs rĂ©plicatifs fondĂ©s sur le virus de lastomatite vĂ©siculaire [14] ou le virus attĂ©-nuĂ© de la rougeole utilisĂ© pour la vaccinationcontre ce virus, vecteurs au sein desquels estplacĂ© le gĂšne de la spicule du SARS-CoV-2.Ces vaccins sont en dĂ©but de test clinique.
âą Enfin une stratĂ©gie attractive consiste enlâemploi de la protĂ©ine spicule recombinanteproduite en lignĂ©es cellulaires et associĂ©eĂ un adjuvant lipidique [15, 16]. Ce vaccinpeut prendre la forme de pseudo particulesvirales, stratĂ©gie efficace dans le cadre dela vaccination contre le virus de lâhĂ©patiteB. Des modifications ont Ă©tĂ© apportĂ©es Ă laprotĂ©ine S pour la stabiliser dans sa formetrimĂ©rique a priori la plus immunogĂšne.DiffĂ©rentes prĂ©parations sont en cours dâĂ©va-luation clinique. . . Le produit de Novavax in-
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duit un titre Ă©levĂ© dâanticorps neutralisantschez les sujets vaccinĂ©s lors des essais dephase I [2].
3. Questions en suspens
Il est bien difficile de prĂ©dire quel(s) sera(ont) in fine,la(es) stratĂ©gie(s) la(es) plus efficiente(s). On ne peutque se rĂ©jouir de la diversitĂ© dâapproches qui aug-mente bien sĂ»r dâautant les chances de succĂšs. Ă cestade, on sait que plusieurs de ces vaccins induisentchez lâhomme la production dâanticorps neutrali-sants lâinfection virale tels que mesurĂ©s in vitro, Ă des titres apparemment comparables Ă ceux des sĂ©-rums de sujets convalescents du Covid-19 [2, 3, 17].Ils induisent aussi une rĂ©ponse T au moins CD4 detype Tfh (follicular helper) nĂ©cessaire Ă la produc-tion dâanticorps, et de type TH1 mais non TH2, ce quipourrait contribuer Ă une meilleure protection dansle temps et Ă©viter des effets dĂ©lĂ©tĂšres des rĂ©ponses detype TH2 (anaphylaxie, inflammation) [18].
Il faut cependant remarquer que lâon ne peut pourlâinstant Ă©tablir de correspondance entre Ă©ventuelleefficacitĂ© clinique et titre dâanticorps neutralisants(ou fonction de la rĂ©ponse T). On ne connaĂźt pas nonplus la cinĂ©tique de diminution des titres dâanticorps.Sera-t-elle similaire Ă celle des sujets infectĂ©s (plutĂŽtlente chez les sujets malades, rapide chez les sujetsinfectĂ©s de façon asymptomatiques)? [19].
Les stratĂ©gies dĂ©veloppĂ©es pour lâinstant reposentsur des injections intramusculaires des vaccins dece fait peu susceptibles dâinduire une immunitĂ© mu-queuse dont pourtant on connaĂźt lâimportance danslâimmunitĂ© contre les virus respiratoires [20]. Cer-tains types de prĂ©paration pourraient ĂȘtre utilisĂ©s eninhalation, cela fera sans doute lâobjet dâĂ©tudes dansun second temps. Enfin la quasi-totalitĂ© des vaccinsen prĂ©paration (en dehors des virus entiers) utilisecomme antigĂšnes la spicule, la protĂ©ine du virus quipermet de se fixer sur son rĂ©cepteur cellulaire ACE-2. Cette approche est logique car les anticorps neu-tralisants mis en Ă©vidence chez les patients infec-tĂ©s sont dirigĂ©s contre cette protĂ©ine et notamment(mais pas exclusivement) le domaine de fixation aurĂ©cepteur. On ne peut Ă©carter lâintĂ©rĂȘt de lâutilisationdâantigĂšnes complĂ©mentaires comme source dâunerĂ©ponse immune protectrice. Cela pourra ĂȘtre exa-minĂ© dans un second temps.
4. CritĂšres de succĂšs
Une utilisation large dâun vaccin anti SARS-2-CoV-2 impose quâil rĂ©ponde Ă une sĂ©rie de critĂšres dâef-ficacitĂ© et de sĂ©curitĂ© sur lesquels on ne peut en-visager de dĂ©roger malgrĂ© les pressions Ă©ventuelles.LâOrganisation mondiale de la santĂ©, lâAcadĂ©mie desSciences des Ătats-Unis [21] et surtout les autoritĂ©srĂ©glementaires qui dĂ©livrent les autorisations dâutili-sation : FDA (food and drug administration aux Ătats-Unis), EMA en Europe ont Ă©mis des recommanda-tions trĂšs prĂ©cises. De nombreux points sont Ă consi-dĂ©rer, outre bien sĂ»r la qualitĂ© du produit vaccinal, enpremier lieu les questions de sĂ©curitĂ© : la rĂ©action im-mĂ©diate (ârĂ©actogĂ©nicitĂ©â) est-elle tolĂ©rable et quelest le risque dâĂ©vĂ©nements indĂ©sirables graves? Sepose la question dâune aggravation de la maladie parlâeffet dâanticorps non neutralisants qui pourraientsoit faciliter lâinfection des macrophages, soit faciliterune rĂ©ponse inflammatoire exacerbĂ©e. Les lympho-cytes T de type TH2 pourraient aussi y contribuer. Cerisque nâest pas que thĂ©orique puisquâil a Ă©tĂ© observĂ©lors de seconde infection par le virus de la dengue(arbovirose) et lors de lâessai dâun vaccin contre ladengue [18] et expĂ©rimentalement avec des prĂ©pa-rations vaccinales contre dâautres coronavirus. Uncertain nombre dâĂ©lĂ©ments laisse nĂ©anmoins pen-ser que ce risque est faible dans le cadre du SARS-CoV-2. Les donnĂ©es de vaccination chez lâanimal sontaussi encourageantes. Reste Ă observer la sĂ©curitĂ©lors des essais de phase III sur ce plan comme sur ce-lui dâautres Ă©vĂšnements. Une surveillance attentivedevra ĂȘtre maintenue ensuite en particulier du fait ducaractĂšre trĂšs innovant de certains des vaccins. Il estessentiel de pouvoir rassurer le public sur la sĂ©curitĂ©de ces vaccins â mise en perspective avec les bĂ©nĂ©-fices attendus.
LâefficacitĂ© est bien sĂ»r centrale. Mais derriĂšre ceterme se dĂ©clinent plusieurs notions : protectioncontre la forme bĂ©nigne de la maladie, les formessĂ©vĂšres (beaucoup plus rares), durĂ©e de la protec-tion, efficacitĂ© de protection des personnes vulnĂ©-rables notamment des personnes ĂągĂ©es. Enfin cesvaccins sont-ils capables de supprimer (ou au moinsrĂ©duire la transmission du virus) en empĂȘchant larĂ©plication virale au niveau de lâoropharynx? La rĂ©-ponse Ă ces questions et notamment la derniĂšreprendra du temps. Les premiĂšres autorisations ditesdâurgence dĂ©pendront du taux dâefficacitĂ© obtenue,
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dâune tendance Ă la rĂ©duction des infections sĂ©vĂšreset dâun recul minimum dâobservation (2 mois selonla FDA). La compaction du temps de dĂ©veloppementde ces vaccins ne doit pas conduire Ă rogner les cri-tĂšres de jugement de sĂ©curitĂ© et dâefficacitĂ©. Ce nâestquâĂ ce prix que la confiance en cette vaccinationpourra ĂȘtre Ă©tablie. Remarquons que le taux dâeffica-citĂ© annoncĂ© des vaccins Pfizer et Moderna est ob-servĂ© dans la phase prĂ©coce post vaccination, lorsdu pic de la rĂ©ponse immune : quâen sera-t-il dansquelques mois ? De la capacitĂ© des vaccins Ă inter-rompre (rĂ©duire) la chance de transmission du vi-rus dĂ©pendra la possibilitĂ© de casser la pandĂ©mie vialâimmunitĂ© de groupe. Si le vaccin Ă©tait parfaitementefficace [2] il faudrait que 70% de la population soitvaccinĂ©e ! Se pose Ă©galement la nĂ©cessitĂ© Ă©ventuellede revaccination rĂ©guliĂšre en fonction de la durĂ©e delâimmunitĂ© protectrice obtenue.
5. Qui vacciner ?
En fonction des performances des vaccins seront dé-finies les priorités de vaccination. La Haute autoritéde santé en France travaille en particulier sur cettequestion.
Les personnes professionnellement ou sociale-ment exposĂ©es (santĂ©, commerce, enseignement, po-lice, prison, personnes en situation de prĂ©caritĂ©, . . .)apparaissent comme devant ĂȘtre prioritaires. Sâil y ades indices dâefficacitĂ© chez les personnes ĂągĂ©es etvulnĂ©rables, celles-ci devront ĂȘtre vaccinĂ©es en pre-miĂšre ligne. Ce nâest que dans un second temps quele(s) vaccin(s) pourra(ont) ĂȘtre proposĂ©(s) au reste dela population.
6. Produire et distribuer les vaccins
Les besoins en vaccin seront trĂšs importants, idĂ©ale-ment 15 milliards de doses pour vacciner toute la pla-nĂšte en tenant compte du fait que 2 doses seront nĂ©-cessaires pour la plupart des vaccins. MalgrĂ© le faitque les capacitĂ©s de production augmentent, il estestimĂ© quâelles atteindront en 2021 quatre milliardsde doses. . . Se pose donc la question de la distribu-tion des vaccins tant dans ces aspects techniquesque Ă©thiques. Techniques, car certains vaccins nĂ©ces-sitent un stockage Ă â20 °C ou â80 °C ce qui nâestpas sans poser de sĂ©rieux problĂšmes de logistique.
Comment sera organisĂ©e la distribution des vaccins,chaque pays doit sây prĂ©parer.
Les pays riches ont anticipĂ© lâacquisition de vac-cins pour leurs citoyens par des prĂ©achats : 800 mil-lions de doses pour les Ătats-Unis, 5 doses par habi-tant pour la Grande-Bretagne, 400, 000 millions dedoses pour la communautĂ© europĂ©enne. . . Est-ce Ă dire que lâon sâachemine vers une forme de nationa-lisme vaccinal certes comprĂ©hensible mais problĂ©-matique ? [22, 23] En effet le contrĂŽle effectif de lapandĂ©mie implique de vacciner au moins 70â80% detous les habitants de la planĂšte. En lâoccurrence, ef-ficacitĂ© et Ă©thique se conjuguent pour Ćuvrer dansce sens. Comment faire en sorte que ces vaccins de-viennent un bien public? LâOMS propose de vaccinerinitialement 20% des citoyens de tous les pays, maison pourrait aller plus loin et considĂ©rer par exemplede vacciner en premier dans les pays oĂč la pandĂ©mieest la plus forte ? [24] Ă lâinitiative de lâOMS, du CEPI(coalition for epidemic preparedness innovation), duGAVI (global vaccine alliance), a Ă©tĂ© crĂ©Ă© le Covaxdont la France et la communautĂ© europĂ©enne ontĂ©tĂ© dâemblĂ©e des partenaires. Cette structure a pourbut de rassembler les fonds nĂ©cessaires pour rendredisponible lâaccĂšs aux vaccins dans tous les pays dumonde en incluant 50% de pays Ă revenu faible oumoyen. Lâobjectif initial est dâacquĂ©rir 2 milliards dedoses de vaccins. Cette initiative sera-t-elle suffisantepour permettre un accĂšs juste aux vaccins? Il est troptĂŽt pour le dire, pour lâinstant les fonds nĂ©cessairesnâont pas Ă©tĂ© recueillis. Cela dit des initiatives com-plĂ©mentaires de production de vaccins notammenten Inde sont susceptibles de contribuer Ă un meilleurpartage. On souhaiterait un systĂšme de rĂ©gulationet de gouvernance internationale capable dâimposerune telle politique ainsi quâune rĂ©gulation des prixdes vaccins. Une forme de reconstruction politiquede lâOMS serait en ce sens nĂ©cessaire en profitant dela crise du Covid-19 [25â27].
7. Confiance en la vaccination
Une derniĂšre dimension clĂ© du succĂšs de la vacci-nation concerne la confiance en la vaccination. Onsait Ă quel point en France, mais aussi aux Ătats-Unis sâest dĂ©veloppĂ©e au sein dâune fraction de lapopulation et du personnel soignant une rĂ©ticence
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Table 1. Principaux vaccins en Ă©valuation
Principe Adjuvant Compagnie Stade de dĂ©veloppement MĂ©thodologiesdĂ©jĂ utilisĂ©es pourdâautres vaccins
âą Virus inactivĂ© Sel dâalu Sinovac Phase III Oui/nombreux
Sel dâalu Sinopharm Phase III
âą Virus vivant attĂ©nuĂ© â Codagenix SĂ©rum Insti-tute of India
Préclinique Oui/nombreux
âą ARNm spicule nanoparticules lipidiques
PfizerâBioNTech Phase IIIârĂ©sultats prĂ©liminaires Non
â Moderna Phase IIIârĂ©sultats prĂ©liminaires
Curevac Phase III
ARN auto réplicatif Curevac Préclinique
âą ADN plasmidique â Inovio/Genexine Phase I/II Non
⹠Vecteur adénoviralnon réplicatifChimpanzé Ad Astra Zeneca/Oxford Phase III Oui Ebola
Ad 26 Johnson and Johnson/Janssen Phase III Non
Ad 5 Cansino Phase III Non
Gorilla Ad Reithera Phase I No
Ad 5+26 Gamaleya Phase III
âą Spicule recombinantenano particules
Matrix-M Novavax Phase III (début) oui
AS03 Sanofi Phase I
Virus-like particle Medicago Phase I Oui; hépatite B
⹠Vecteur réplicatif
VSV-spicule MSD Phase I Non
Rougeole-spicule â MSD-ThemisâInstitut Pasteur Phase I
Grippe-spicule â Beijing Wantai Phase I
Alu : Aluminium; ad : adenovirus ; vsv : vesicular stomatitis virus.
Ă la vaccination [28, 29]. Des enquĂȘtes dâopinion rĂ©-centes dans le cadre du Covid-19 lâont encore mon-trĂ©. Il est donc crucial que la mise en Ćuvre dâunprogramme vaccinal comporte une sĂ©rie de mesuresvisant Ă Ă©tablir la confiance tant du personnel desantĂ© que des citoyens. Cela passe dâune part parune facilitation pratique de la vaccination : parcourssimplifiĂ©, vaccination par mĂ©decins, pharmaciens etinfirmiers, crĂ©ation de centres de vaccination mo-biles, prise en charge intĂ©grale du cout par la CaisseNationale dâAssurance Maladie, dâautre part par descampagnes dâinformation ciblĂ©es, au contenu clair ettransparent [30]. La sociĂ©tĂ© civile Ă travers de nom-breuses associations impliquĂ©es dans les questionsde santĂ© publique doit ĂȘtre mobilisĂ©e dans la dĂ©fi-nition de cette politique et comme relai mĂ©diatiquedâexplication. Pourrait ĂȘtre mis en avant si un ou plu-
sieurs vaccins empĂȘchent la transmission virale lefait que la vaccination fasse lâobjet dâune attitude al-truiste : la vaccination des uns protĂšge les plus vul-nĂ©rables. Les sciences humaines et sociales doiventpouvoir ĂȘtre mobilisĂ©es pour prĂ©ciser ces modalitĂ©sdâaction et en Ă©valuer lâimpact [31]. La dĂ©monstrationde lâĂ©ventuelle efficacitĂ© ne sera pas sans poser un di-lemme Ă©thique : faut-il proposer le vaccin aux sujetsdu groupe contrĂŽle, au prix dâempĂȘcher toute Ă©valua-tion ultĂ©rieure, ce qui ne serait pas raisonnable [32].Comment envisager de nouveaux essais thĂ©rapeu-tiques dans cette situation? Plusieurs stratĂ©gies pour-ront ĂȘtre envisagĂ©es [33]. Enfin les outils de la mo-dĂ©lisation devraient permettre dâĂ©valuer lâeffet du(es)vaccin(s) sur la pandĂ©mie en fonction de leur effica-citĂ© et leur acceptabilitĂ© [34, 35].
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La mise en place de la vaccination contre le SARS-CoV-2 est une action vitale tant en termes de santĂ©publique que sociĂ©tale et Ă©conomique. Elle ne sauraitĂ©chouer. Lorsquâil aura Ă©tĂ© dĂ©montrĂ© sans Ă©quivoquequâun ou plusieurs vaccins comportent une balancebĂ©nĂ©fice/risque favorable, tout doit pouvoir ĂȘtre misen Ćuvre pour programmer de façon progressive lavaccination des populations et ce Ă lâĂ©chelle interna-tionale. Il ne faut pas confondre vitesse et prĂ©cipi-tation, savoir rĂ©sister aux intĂ©rĂȘts particuliers, maisil sâagit, par une mobilisation mondiale de mettreen Ćuvre une politique commune au service de lasantĂ© publique pour aboutir au contrĂŽle progres-sif de la pandĂ©mie. Il sera essentiel dâeffectuer desĂ©tudes longitudinales des sujets vaccinĂ©s (Ă©tude ditephase 4) pour apprĂ©cier lâefficacitĂ© (et la sĂ©curitĂ© aucours du temps) et ce en fonction des groupes (risqueĂ©levĂ©, . . .), cette Ă©valuation servira de base des prĂ©-visions en termes de nĂ©cessitĂ© de revaccination etdâĂ©volution de la pandĂ©mie [35].
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[5] H. Wang, Y. Zhang, B. Huang, W. e. a. Deng, âDevelopmentof an inactivated vaccine candidate, BBIBP-CorV, with potentprotection against SARS-CoV-2â, Cell 182 (2020), p. 713-721e9.
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