bubonic 3

7/29/2019 Bubonic 3

1/22

Lecture 11 - Herd Immunity

7/29/2019 Bubonic 3

2/22

Ro - the average number of new infections from 1infected individual in a population of

fully susceptible hosts.

Ro> 1

Time

R - effective growth rate

of the disease.

7/29/2019 Bubonic 3

3/22

Ro - the average number of new infections from 1infected individual in a population of

fully susceptible hosts.

Ro> 1

Time

R - effective growth rate

of the disease.

7/29/2019 Bubonic 3

4/22

R = Ro S/N

If a sufficiently high proportion of the population is immune,

then R will be below 1 and the disease cannot circulate.

ie for control R

7/29/2019 Bubonic 3

5/22

Herd Immunity

A type of community protection from disease that occurswhen the vaccination of a portion of the population (or

herd) provides protection to unvaccinated individuals by

making it less likely that any infected individual will

contact a susceptible individual and thus pass on the

disease

7/29/2019 Bubonic 3

6/22

R = Ro S/N

If a sufficiently high proportion of the population is immune,

then R will be below 1 and the disease cannot circulate.

ie for control R

7/29/2019 Bubonic 3

7/22

Ro> 1

P > 1( 1/ Ro)

Criteria for eradication by vaccination

Where P is the proportion that must be

vaccinated to eliminate the disease.

Ro (1P) < 1

Time

7/29/2019 Bubonic 3

8/22

20

10

15

5

0

Ro

Measles

Chicken

Pox

Polio

Smallpox

InfluenzaEbola

90-95%

85-90%

85%

80%50%

33%

Data from Anderson & May 1992

P > 1( 1/ Ro)

7/29/2019 Bubonic 3

9/22

93

80

88

90

95

83

79

78

8477

Smallpox vaccination rates in West AfricaOctober 1974 to September 1975

Data from Arita et al. 1986

7/29/2019 Bubonic 3

10/22

Country Period Reason Consequence

Holland 1999 Religious 2961 cases and 3 deaths

Ireland 2000 Health risk 300 cases and 3 deaths

Nigeria 2001 Religious/

political

20,000 cases and 600 deaths in 3

months of 2005

USA 2005 Health risk 34 cases (largest outbreak since

1996)

France

etc

2011 Religious &

Health risk

26,000 cases and 11 deaths

Examples of declines in measles vaccination rates

7/29/2019 Bubonic 3

11/22

7/29/2019 Bubonic 3

12/22

The Headlines

Do Measles VaccinesPut Children At Risk

For Autism?

Measles vaccinelinked to autism?

The Study

7/29/2019 Bubonic 3

13/22Copyright 2005 BMJ Publishing Group Ltd.

Gupta, R. K et al. BMJ 2005;330:1132-1135

Fig 2 Mumps notifications and confirmed cases, 1995-2004 by quarter

7/29/2019 Bubonic 3

14/22

If God had decreed from all eternity that a certain

person should die of smallpox, it would be a frightful

sin to avoid and annul that decree by the trick ofvaccination.

Timothy Dwight IV, Minister and President of Yale

University

7/29/2019 Bubonic 3

15/22

Name Established

Anti-vaccination Society 1798

Anti-Compulsory Vaccination League 1866

The Anti-Vaccination Society of America 1879

New England Anti-Compulsory Vaccination League 1882Anti-Vaccination League of New York City 1885

London Society for the Abolition of Compulsory Vaccination 1880

The National Anti-Vaccination League 1896

The British Anti-Vaccination

League encouraged the public to

obtain smallpox vaccinationexemptions.

7/29/2019 Bubonic 3

16/22

The term "conscientious objector" originally referred to opponentsof England's aggressively-enforced smallpox vaccination

requirement in the late nineteenth century.

Durbach, N. in : Class, Gender, and the Conscientious Objector to

Vaccination, 1898-1907.

Conscientious Objectors at a

quarry works near Aberdeen,

October 1916.

7/29/2019 Bubonic 3

17/22

Seat belts do not cause reckless driving, tetanus shots do not cause

children to see out rusty nails, and hepatitis B vaccination has notaltered sexual practices or increased injection-drug abuse in any

population. Dr. Bradley Monk, UC Irvine

7/29/2019 Bubonic 3

18/22

Ro = contacts per unit time

x

transmission probability

x

duration of infectiousness

7/29/2019 Bubonic 3

19/22

20

10

15

5

0

Ro

Measles

Chicken

Pox

Polio

Smallpox

InfluenzaEbola

90-95%

85-90%

85%

80%50%

33%

Data from Anderson & May 1992

P > 1( 1/ Ro)

7/29/2019 Bubonic 3

20/22

Ro = contacts per unit timex


x


Measles

Medium

High

Low

Ro = 11-18

7/29/2019 Bubonic 3

21/22



x


Influenza

Medium

Medium

Low

Ro = 2-10

7/29/2019 Bubonic 3

22/22



x


Ebola

Low

Low

Low

Ro < 1
http://upload.wikimedia.org/wikipedia/commons/a/ab/7042_lores-Ebola-Zaire-CDC_Photo.jpg

bubonic 3

Documents