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The influenza virus never seems to go away. This virus survives and causes
misery for us every year because of its ability to quickly mutate. It can even
incorporate genetic material from animal-sourced influenza strains to form new
ones our immune systems have never battled before.
There’s been four global influenza pandemics in
recent history, starting with the devastating
Spanish Flu of 1918 that infected an
estimated 500 million people worldwide.
This represented about one-third of the
planet’s population the early 20th
century.1 The Spanish Flu contributed to
the death of 20 to 50 million victims
worldwide, including about 675,000
Americans.1
Well over a decade ago, researchers were able to retrieve viable Spanish Flu viral
proteins from preserved, long-deceased victims and soon learned why the
Spanish Flu was so deadly: A group of three genes within the virus critically
weakened the victim’s pulmonary tissue. This rapid and severe lung damage led
to pulmonary edema or instead, offered a gateway for bacterial pneumonia to
quickly set in and cause death.2 Sir Alexander Fleming did not discover penicillin
until much later in 1928, so the bacterial pneumonia was still untreatable by
what we take for granted today: Antibiotics.
Influenza The flu season approaches: Influenza Type A and Type B viral infections
1 to 4 days from exposure
3 days to more than 2 weeks
Respiratory droplets
Gloves, N95 mask, goggles,
disposable gown or Tyvek suit.
Resides in respiratory tissue
and can be transmitted
through a cough, sneeze,
talking, or other respiratory
secretion release.
Can survive on room air
temperature surfaces for
hours to a full day depending
on the porosity of surface,
temperature, and humidity.
Use standard EMS/hospital
disinfecting solutions to clean.
Is a virus, so does not produce
disinfectant-resistant spores.
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While not as catastrophic as the Spanish Flu, the remaining global influenza pandemics that also affected the
United States included:
• The Asian flu pandemic (H2N2), which occurred between 1957 and 1958 and killed about 1.1 million
people worldwide, including some 116,000 people in the United States.3
• The Hong Kong flu (H3N2) pandemic from 1968 to 1969 killed approximately 1 million people,
including about 100,000 Americans.4
It is believed that the Hong Kong flu and the earlier Asian flu were mutations of an avian (bird) flu
virus and began spreading in the United States by infected soldiers returning home from the Vietnam
War. By that time, the virus had already spread from China to other east Asian areas, including
Vietnam and Singapore. The availability of antibiotics helped to reduce mortality from secondary
bacteria pneumonia infections, but the fatality rate was still significant. Flu pandemics tend to form
waves of increased infection, and the last wave was particularly severe on global mortality.
• Swine Flu (2009 Human H1N1): In just over a year, more than 12,000 Americans perished during
the H1N1 (or “swine flu”) pandemic that lasted 19 months. It was discovered in January 2009 and
finally reduced to sporadic (smoldering) cases in August 2010.5
This flu was a little different ---
death was more likely in those who
were younger compared to the
Asian and Hong Kong flu… usually
less than 65 years old. It was first
discovered in central Mexico and
within a few months spread to 43
countries, including the US.6
Researchers suspect that older
Americans may have developed
some faint immunity decades
before through exposure to another
influenza strain much like this one.
However, the 2009 H1N1 pandemic
did contribute to the death of
young and old alike.
In the past, a few flu strains had
already developed from a triple
reassortment of avian (bird), swine
(pig), and human flu viruses.
However, the 2009 Human H1N1
“swine flu” evolved as a novel (new)
virus when an existing
The H1N1 Swine Flu ancestry tree. The Eurasian swine viral component
combined with previous avian/swine/human influenza viruses to form
H1N1. This created a new (novel) virus and is now one of the strains
targeted by our flu vaccines. Image: Trifonov (2009).
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avian/swine/human influenza strain added genetic material from a Eurasian pig flu virus.6 The name
“swine flu” refers to this Eurasian swine addition.
Both the swine H1N1 and human H3N2 virus strains are two type A influenza viruses targeted by the
annual influenza vaccine.
The signs and symptoms associated with influenza include one or more of the following:7
• Fever or feeling feverish/chills. Presence of a fever or chills is not a requirement though.
• Cough
• Sore throat
• Runny or stuffy nose (rhinorrhea)
• Muscle or body aches; Headaches
• Fatigue (tiredness)
• Some people may have vomiting and diarrhea. This is usually more common in children.
The CDC’s chart of emergency warning signs for flu. While the flu usually resolves on its own without
complications, the warning signs above suggest a more emergent condition. Image: CDC.
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Is it just the common cold or influenza? The flu’s signs and symptoms are nearly interchangeable
with the milder common cold. Both are respiratory illnesses but caused by entirely different viruses.
Generally, the flu’s symptoms
appear rapidly, are more severe,
and can contribute to serious
health problems (pneumonia,
sepsis, myocardial injury) leading
to hospitalization or even death.
The common cold usually has a
gradual onset, is more likely to
cause rhinorrhea (runny nose),
and its symptoms are milder with
less effect on a person’s overall
health.8
Recovery from the flu usually
takes a few days to two weeks or
more. Some people may develop
complications that are short-lived
or instead, can lead to permanent
disability or even death.
Some of the complications with flu are listed below. Some are uncommon, but should remain in the back
of your mind when caring for a patient who “has the flu” but appears to be more critically ill: 7
• Sinus and ear infections
• Pneumonia (either from the flu or co-infection with an opportunistic bacterial infection)
• Myocarditis (inflammation of the heart tissue)
• Encephalitis (inflammation of brain tissue)
• Rhabdomyolysis (breakdown of skeletal muscle tissue)
• Multiorgan failure (lungs, kidneys, etc.)
• Extreme inflammatory response can lead to sepsis (hypotension as a sign, for example)
• Worsening of chronic medical conditions, such as asthma or heart failure.
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Influenza is transmitted by respiratory droplets. A person cannot acquire swine flu by eating pork or
avian flu by eating chicken or eggs. The highest risk of transmission occurs when an infected person
sneezes, coughs, or transmits respiratory secretions into the air by other means. Transmission can also
occur indirectly through contact with contaminated surfaces such as tables, pens, etc. where the virus is
then brought into the nose or mouth. However, this route is not as common compared to respiratory
droplets in the air.
The time from infection to illness (incubation
period) is about 2 days, but ranges from one
to four days.9
How contagious is it? Back in 1918
with the Spanish Flu pandemic, it’s
estimated that one person typically infected
1.4 to 2.8 others.10 More recently with the
swine flu in 2009, one person infected about 1.4
to 1.6 other people.11 This reduction was credited
towards flu vaccines and the use of antivirals that helped
lower the risk of infecting others.
With COVID-19 still a continuing threat that is not disappearing anytime soon, UMC EMS’ PPE
requirements remain at the same level for those with suspected COVID-19: Gloves, N95 mask, eye
goggles/face shield, and Tyvek suit. Both COVID-19 and influenza present similar (if not identical) signs
and symptoms, and the only true way to determine the causative agent is through diagnostic testing.
All contact surfaces must be disinfected thoroughly before returning to service. This includes the pulse
oximeter (use alcohol only), ECG cables, BP cuff(s), and stethoscopes. Door handles, the radio
microphone, and cabinet doors are easily forgotten contaminated areas.
How long can influenza survive? The influenza virus can remain viable on contact surfaces for
hours. One study that examined the viability of H1N1 swine flu influenza and found the virus survived in
an indoor-type, temperate environment for up to a few hours on porous surfaces (cloth, paper). Rarely,
it survived more than nine hours on most of the other surfaces tested. But, metallic and non-metallic,
non-porous materials (countertops and door handles, for example) posed the greatest risk with the virus
surviving up to 24 hours in some samples.12
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The annual influenza vaccination is not 100% effective. However, the Centers for Disease Control and
Prevention (CDC) also reports:
“…Flu vaccination reduces the risk of flu illness by
between 40% and 60% among the overall population
during seasons when most circulating flu viruses are
well-matched to the flu vaccine. In general, current flu
vaccines tend to work better against influenza B and
influenza A(H1N1) viruses and offer lower protection
against influenza A(H3N2) viruses.” 13
Other vaccines such as hepatitis, varicella, or tetanus are far more effective in targeting their specific
pathogen. Influenza vaccination is less effective because how our immune system responds to flu and
more importantly, one trait that allows influenza to adapt and survive well: Antigenic drift.
Antigenic drift refers to the small changes or
mutations in the genetic makeup of a virus
that inevitably alters its surface glycoproteins.
The surface proteins are called antigens,
which is what our immune system can use as
a form of identification to determine if
something is friend or foe. After vaccination
or exposure to a virus, antibodies are
developed to target specific viral antigens and
trigger an immune response.
Vaccines focus on certain unique antigens
found on a pathogen. However, the influenza
virus --- particularly type A ones --- quickly mutate and our immune system may not be able to recognize
it from a previous vaccination or infection.
Antigenic drift is also the reason why a person can be re-infected by the influenza virus within the same
year or even more frequently. Just a small yet effective change in the antigen can be enough for it to
look like something the immune system has not encountered before.
The flu vaccine is reviewed and updated yearly to try and keep up with antigenic drift. But even if a
vaccine is not a perfect match for the season’s flu, if it’s close, there could be enough antibody protection
to help reduce the severity of the signs and symptoms. Vaccination has been shown to effectively reduce
hospitalization and ICU care for those who acquired the flu even after receiving the vaccine that year.14
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Antigenic shift is different than antigenic drift. In
this case, there is an abrupt, major change in the
influenza virus. For example, if an influenza virus
from an animal population gains an ability to
infect humans, antigenic shift occurs. The 2009
swine flu is a recent case where the addition of a
Eurasian swine flu created a new H1N1 strain
unrecognizable to nearly everyone’s immune
system. This resulted in a pandemic. Fortunately,
antigenic shift does not happen frequently.
Types of flu. In the United states, influenza in
humans is usually caused by either Type A or Type
B flu. There is a Type C, which is uncommon and
presents with milder symptoms), and so is not the target of vaccination programs. Type D influenza
remains infective for animals only, particularly cattle.
Type A flu is usually implicated for both epidemics and pandemics as it quickly mutates (antigenic drift)
and can even incorporate other genetic material from vastly different flu strains (antigenic shift). Annual
vaccinations protect against two of the more common strains of Type A flu. Type B flu does not shift (it
affects humans only) and it does not drift much at all. Symptoms of Type B influenza infection may even
be milder in adults compared to Type A flu. However, it tends to develop more serious illness and
complications in children, which is why flu vaccines for healthcare providers include the two more
common Type B strains within their composition.
Vaccination recommendations. An annual flu vaccination is recommended for everyone 6
months old or older. During 2018, vaccination prevented an
estimated 4.4 million influenza illnesses, 58,000 influenza-
associated hospitalizations, and 3,500 influenza-associated
deaths in the United States alone.15
It takes about two weeks for enough antibodies to develop
after vaccination to provide protection against the flu. If
someone develops the flu a few days after vaccination, they did
not “get the flu” from the vaccine. They acquired the flu before
enough antibodies were produced to combat it. The injectable
flu vaccine does not have any viable or living flu virus that can
cause illness, so it cannot cause the flu.
Can a person be contagious before flu symptoms develop? Yes. The flu can be transmitted one day
before the infected person shows any signs or symptoms.15
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Keep in mind that some people can still become infected with a flu virus the vaccine was designed to
protect against. Protection provided by flu vaccination can vary widely, based in part on health and age
factors of the person getting vaccinated. In general, a flu vaccine works best for healthy younger adults
and older children. Some older adults and those with certain chronic illnesses may require a stronger or
double dose of the flu vaccine to account for their less-than-optimal immune system.
While the flu vaccination is not a perfect tool, it is still the best way to protect against flu infection along
with frequent hand washing, PPE, and disinfecting surfaces after each patient contact in the ambulance.
Be sure to complete the quiz and evaluation to earn credit for this education.
Please let a member of the training staff know of any questions. Thank you!
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1 1918 Pandemic (H1N1 virus). Centers for Disease Control and Prevention. Last review: March 20,
2019. Web page: https://www.cdc.gov/flu/pandemic-resources/1918-pandemic-h1n1.html.
Accessed: August 30, 2020.
2 Jordan D, Tumpey T, Jester B. The Deadliest Flu: The Complete Story of the Discovery and
Reconstruction of the 1918 Pandemic Virus. Centers for Disease Control and Prevention. Last
review: December 17, 2019. Web page: https://www.cdc.gov/flu/pandemic-
resources/reconstruction-1918-virus.html. Accessed: August 30, 2020.
3 1957-1958 Pandemic (H2N2 virus). Centers for Disease Control and Prevention. Last review: January
2, 2019. Web page: https://www.cdc.gov/flu/pandemic-resources/1957-1958-pandemic.html.
Accessed: August 30, 2020.
4 1968 Pandemic (H3N2 virus). Centers for Disease Control and Prevention. Last review: January 2,
2019. Web page: https://www.cdc.gov/flu/pandemic-resources/1968-pandemic.html. Accessed:
August 30, 2020.
5 2009 H1N1 Pandemic (H1N1pdm09 virus). Centers for Disease Control and Prevention. Last review:
June 11, 2019. Web page: https://www.cdc.gov/flu/pandemic-resources/2009-h1n1-pandemic.html.
Accessed: August 30, 2020.
6 Trifonov V, Khiabanian H, Rabadan R. Geographic dependence, surveillance, and origins of the 2009
influenza A (H1N1) virus. N Engl J Med. 2009;361(2):115-119. doi:10.1056/NEJMp0904572
7 Flu Symptoms & Complications. Centers of Disease Control and Prevention. Last update: July 2,
2020. Web site: https://www.cdc.gov/flu/symptoms/symptoms.htm. Accessed: August 29, 2020.
8 Influenza (flu). Centers for Disease Control and Prevention. Last review: December 30, 2019. Web
page: https://www.cdc.gov/flu/symptoms/coldflu.htm. Accessed: August 30, 2020.
9 Influenza (seasonal). World Health Organization. November 6, 2018. Web page:
https://www.who.int/en/news-room/fact-sheets/detail/influenza-(seasonal). Accessed: August 31,
2020.
10 Ferguson NM, Cummings DA, Fraser C, et al. Strategies for mitigating an influenza pandemic. Nature.
2006; 442:448-452.
11 Coburn, BJ, Wagner BG, Blower S. Modeling influenza epidemics and pandemics: insights into the
future of swine flu (H1N1). BMC Med. 2009; 7 (30). doi: 10.1186/1741-7015-7-30
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12 Greatorex JS, Digard P, Curran MD, et al. Survival of influenza A(H1N1) on materials found in
households: implications for infection control. PLoS One. 2011;6(11):e27932.
doi:10.1371/journal.pone.0027932
13 Vaccine Effectiveness: How Well Do the Flu Vaccines Work? Centers for Disease Control and
Prevention. Last reviewed: January 3, 2020. Web page: https://www.cdc.gov/flu/vaccines-
work/vaccineeffect.htm. Accessed: August 31, 2020.
14 Thompson MG, Pierse N, Sue Huang Q, et al. Influenza vaccine effectiveness in preventing influenza-
associated intensive care admissions and attenuating severe disease among adults in New Zealand
2012-2015. Vaccine. 2018;36(39):5916-5925. doi:10.1016/j.vaccine.2018.07.028
15 Centers of Disease Control and Prevention. Key Facts About Seasonal Flu Vaccine. Last update:
August 17, 2020. Web site: https://www.cdc.gov/flu/prevent/keyfacts.htm. Accessed: August 29,
2020.
Trifonov V, Khiabanian H, Rabadan R. Geographic dependence, surveillance, and origins of the 2009
influenza A (H1N1) virus. N Engl J Med. 2009;361(2):115-119. doi:10.1056/NEJMp0904572
Flu Symptoms and Complications. Centers for Disease Control and Prevention. Last review: July 2, 2020.
Web page: https://www.cdc.gov/flu/symptoms/symptoms.htm. Accessed: August 31, 2020.