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To Vaccinate or Not to Vaccinate?

To Vaccinate or Not to Vaccinate?. That is the question. Joanne Mann J.L.Mann@Massey.ac.nz. Cholera Dengue Diphtheria E coli Influenza Haemophillus influenzae B Hepatitis A Hepatitis B Human Papillomavirus Japanese encephalitis Measles Meningococcus Mumps

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To Vaccinate or Not to Vaccinate?

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  1. To Vaccinate or Not to Vaccinate? That is the question Joanne Mann J.L.Mann@Massey.ac.nz

  2. Cholera Dengue Diphtheria E coli Influenza Haemophillus influenzae B Hepatitis A Hepatitis B Human Papillomavirus Japanese encephalitis Measles Meningococcus Mumps Tetanus/Neonatal tetanus Pertussis (whooping cough) Pneumococcus Poliomyelitis Rabies Rotavirus Rubella Shigella Smallpox Tuberculosis Typhoid Yellow fever Varicella (chickenpox) Vitamin A Other diseases Vaccine-Preventable Diseases* *Source: http://www.who.int/vaccines/en/vaccprevdis.shtml To Vaccinate or Not to Vaccinate?

  3. Why Be Vaccinated? • So that you don’t get infected. • So that you don’t pass the infection on. • But… • What about the negative side effects from a vaccination? To Vaccinate or Not to Vaccinate?

  4. Should I be Vaccinated? • It depends on the relative costs of remaining susceptible and of being vaccinated. • But, if everyone around you is vaccinated… To Vaccinate or Not to Vaccinate?

  5. On To the Maths… • Let p be the proportion of the population that are vaccinated (then 1-p aren’t vaccinated). • Let Cvbe the cost of being vaccinated, and Cs be the cost of remaining susceptible. • Let S∞be the proportion of the population that are still susceptible after an epidemic. To Vaccinate or Not to Vaccinate?

  6. On To the Maths… • S∞ is calculated from • R0is the basic reproduction ratio: the number of secondary cases that would occur from a primary case in a fully susceptible population. To Vaccinate or Not to Vaccinate?

  7. Two Choices • Be vaccinated, then your expected individual cost is Cv. • Remain susceptible, then your expected individual cost is 1-p-S∞ is the proportion of the population who were infected during the epidemic. To Vaccinate or Not to Vaccinate?

  8. The Community • The cost to the community will be a combination of the two individual strategies: • What is the best option? To Vaccinate or Not to Vaccinate?

  9. To Vaccinate or Not to Vaccinate?

  10. The Best Individual Strategy • The best strategy for the individual varies depending on Cv and Cs. • If Cv < Cs then the expected cost of vaccination is lower than the cost of remaining susceptible, unless a significant proportion of the population is vaccinated. • Best Strategy: To Vaccinate or Not to Vaccinate?

  11. Best for the Community • The lowest expected cost, for the community, is to always vaccinate the proportion of the population equal to • So, convince every one you come in contact with to be vaccinated – then you don’t have to be! To Vaccinate or Not to Vaccinate?

  12. References • Bauch, C. T., Galvani, A. P. and Earn, D. J. Group Interest Versus Self-Interest in Smallpox Vaccination Policy.Proc Natl Acad Sci U S A. 2003 Sep 2;100(18):10564-7 (available online: http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12920181) • Mann, J. Modelling repeated epidemics with general infection kernels. To Vaccinate or Not to Vaccinate?

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