In this lecture, we delve into the fundamental concepts of vaccination and herd immunity, essential components in public health strategies to combat infectious diseases. Vaccination, a cornerstone of preventive medicine, involves the administration of vaccines to induce immunity against specific pathogens. Herd immunity, on the other hand, refers to the indirect protection that occurs when a significant proportion of the population becomes immune to a contagious disease, thereby reducing its transmission within the community.

1. Public Health
Microbiology
Vaccination & Herd Immunity
Dr Jasmine E Khairat

2. Learning Objectives
• Define herd immunity and explain the importance of vaccination
campaigns to maintain herd immunity
• Define attenuation and describe different methods to produce attenuated
pathogens
• Compare contrast the nature and usefulness of the different types of
vaccines discussed: Attenuated, Inactivated, Subunit, Conjugate and
genetically engineered; provide examples for each type of vaccine.
• Describe the function of adjuvants in vaccines

3. Control Measures Applied to the Host: Active Immunization
3
vaccination is:
the process of administration of an antigen.
immunization is:
the development of a specific immune
response.

4. VACCINES

5. Watch this video https://youtu.be/-muIoWofsCE
How
Vaccines
Work

6. Principles of
Vaccination
• Self vs. nonself
• Protection from infectious
disease
• Response indicated by the
presence of antibody
• Very specific to a single
organism

7. Principles of Vaccination
Active immunity Passive immunity

8. Effectiveness
of vaccination
for some
common
infectious
disease
8

9. Malaysia's National Immunisation Programme. Graphic by Ministry of Health. https://mypositiveparenting.org/wp-content/uploads/2022/05/NIP-Table3_ol-690x326.jpg
Malaysia's National Immunisation Programme

10. https://clinicalinfo.hiv.gov/en/glossary/acquired-immunity
Goldsby RA, Kindt TJ, Osborne BA. Vaccines (chap 18). In Kuby Immunology, 4th ed,
2000. W. H. Freeman & Co, New York, NY; pp. 449-465.

11. TYPES OF VACCINES

12. Types of Vaccines
https://vaccine-safety-training.org/live-attenuated-vaccines.html

13. Types of Vaccines
• Passive – injection of immunoglobulins, short immunity
• Inactivated (killed) – limited immune response
• DNA – Plasmid containing DNA that codes for desired antigen
• Attenuated – large response and reversion to virulence
• Recombinant – live or inactivated
• Transvected – insertion of antigen into carrier (e.g., yeast)
• Conjugate
• Vector – insertion of gene into a carrier/vector agent
• Toxoids – block toxin but not infection
• Subunit – components of agent

14. 14
Active Immunization:
Types of Antigens (continued)

15. Let’s make vaccines!
• NOVA - Official Website | Making
Vaccines - PBS
• https://www.pbs.org/wgbh/nova/body/
making-vaccines.html

17. Vaccine Ingredients
• Antibiotics
• Egg protein
• MSG
• Thiomerosal

18. VACCINE EFFICACY

19. VE
• VE is measured by calculating the risk of
disease among vaccinated and
unvaccinated persons and determining
the percentage reduction in risk of
disease among vaccinated persons
relative to unvaccinated persons.
• The greater the percentage reduction of
illness in the vaccinated group, the
greater the vaccine
efficacy/effectiveness.

20. Vaccine efficacy or vaccine effectiveness (VE)

21. Active Immunization:
Calculation of Vaccine Efficacy
• Vaccine efficacy/effectiveness is interpreted as the proportionate reduction in disease among the
vaccinated group.
• Formula for calculation of vaccine efficacy (VE):
VE = Attack rate in Unvaccinated – Attack rate in Vaccinated
Attack rate in Unvaccinated
VE of 90% indicates a 90% reduction in disease occurrence among the vaccinated group
or
90% reduction from the number of cases you would expect if they have not been vaccinated.

22. Calculating Risks
• In an outbreak of Varicella (chickenpox) in Seattle in 2022, it was diagnosed in 18 out
of 152 vaccinated children compared to 3 of 7 unvaccinated children.
• Calculate the risks.
Varicella Non Case Total
Vaccinated 18 134 152
Unvaccinated 3 4 7
Total 21 138 159
Table 1 Incidence of Varicella among Schoolchildren in 9 affected classrooms – Seattle 2022
Risk of varicella among vaccinated children =
Risk of varicella among unvaccinated children =

23. Required Steps for
Vaccine Approval
• Basic laboratory research
• Preclinical – growth in tissue
culture systems and animal
testing for immunogenicity and
safety; challenge testing in
animals
• Investigational New Drug
(IND) application sponsor
submits proposal for testing in
humans
• Clinical Trials

25. https://www.bactivax.eu/blog/the-process-of-designing-and-testing-a-vaccine

26. HERD IMMUNITY

27. Active Immunization:
Herd Immunity
• Besides protection of the individual, vaccination may also provide a degree
of community protection called herd immunity
• Herd immunity:
The relative protection of a population group achieved by reducing or
breaking the chains of transmission of an infectious agent because most of
the population is resistant to infection through immunization.

28. Active Immunization:
Herd Immunity
The mechanisms of herd immunity include:
– Direct protection of vaccinees against disease or transmissible infection
– Indirect protection of nonrecipients by virtue of surreptitious vaccination
(e.g., spread of attentuated vaccines), passive antibody, or just reduced
sources of transmission
– Level to achieve herd immunity depends on infectiousness of agent

29. high proportion of individuals with
immunity protect the vulnerable
members of population
Ro
Herd Immunity threshold
Image by NIAID is licensed under https://creativecommons.org/licenses/by/2.0/

30. What is herd Immunity
Watch this video https://www.youtube.com/watch?v=cEn1PKyBUNc

31. Herd Immunity
Threshold
Proportion of the population
that must be immune in order
to prevent the disease from
spreading from person to
person

32. Herd Immunity Threshold
• HIT (denoted qc) can then be calculated with the reproduction number:
qc = [1 − 1/R0]*100
• qc gives the percentage of fully immune people required to stop the spread of
the disease.
Caveat:
• In real life scenarios, neither disease- nor vaccine-conveyed immunity is ever
quite 100%, and this has to be accounted for by introducing the factor VE –
vaccine efficacy

33. Herd Immunity Threshold
• Example:
For measles, which has a reproduction number 12, and when we
factor in vaccine efficacy (VE), which for measles is ~97 %, we get the
vaccine coverage (Vc) necessary for herd immunity, (qc), by the
following formula:
Vc =qc/VE
Vc =(1-1/12)/97%
= 95%
So, roughly 95 % measles vaccine coverage is necessary to stop the spread
of measles in a population.

34. TEST YOURSELF
Assume that Ebola has a basic case reproduction
number (R0) of 2. What percentage of the
population must be immune in order to reach the
herd immunity threshold?

35. Herd Immunity Threshold
The percentage of the population that needs to be vaccinated to reach the
herd immunity threshold (the vaccine coverage) depends on the vaccine
efficacy.
Assume a vaccine for Ebola is available with an efficacy of 75%, and that the R0
for Ebola is 2.
What proportion of individuals must be vaccinated in order to reach the herd
immunity threshold?

36. Estimated R0 and HITs of well-known infectious diseases
inadequate immunization rates threaten herd immunity
Disease Transmission R0 HIT
Measles Airborne 12-18 92-95%
Pertussis Airborne droplet 12-17 92-94%
Diphtheria Saliva
6-7 83-86%
Rubella
Airborne droplet
Smallpox
5-7 80-86%
Polio Fecal-oral route
Mumps
Airborne droplet
4-7 75-86%
SARS 2-5 50-80%
Ebola
(Ebola virus epidemic - West Africa)
Bodily fluids 1.5-2.5 33-60%
Influenza
(Influenza pandemics)
Airborne droplet 1.5-1.8 33-44%

37. Decline in measles incidence after approval of measles vaccine in USA

38. Misinformation about the risks of vaccines has led
to increase in disease as herd immunity is lost
Parham Fig. 11.24
False claims were made of link between mercury in MMR and autism
Evidence shows no link between MMR vaccine and autism

39. Vaccination—and any associated risk—is
better than not vaccinating at all. Do you
agree with this statement?