BIO220H1 Lecture Notes - Lecture 26: Smallpox Vaccine, Cirrhosis, Edward Jenner
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April 2nd 2020
BIO220 LEC0101
BIO220 Lecture 26: Evolutionary Medicine
Vaccine
- Initiate an immune response
- Memory cells form to improve immune response the next time the body encounter a
similar antigen
Smallpox
- Orthodox disease
- First human eradicated disease
- Last case in Canada was in 1946 and in the world in 1977
- Smallpox vaccine came from milkmaids who were immune to smallpox
- Milkmaids get a much less virulent form of the disease
- Edward Jenner exposed patients to puss from blisters of infected smallpox milkmaids –
successfully protected patients from the deadly smallpox
Evolution in vaccine
- Antibiotics are failing due to increase frequency of evolution, and so does vaccines
- Immune systems do massive selection on pathogens
- Initiate an immune response – (vaccination) – potential selection on pathogens
- Only three cases were shown to not be effective with vaccines
Two cases studies
1) Hepatitis B
- Major cause of liver cirrhosis, liver cancer, and hepatitis
- Vaccine targets the ‘a’ determinant surface protein of the virus
- In the 1990s, vaccine resistance → individual that had the vaccine still got the infection
- Mutation in the virus seem to correlate with the infection – changed the structure of the
antigen, and now unable to be seen by the immune cells.
- The frequency of the mutant allele increased over time in vaccinated people – evolution!
- BUT! This didn’t cause a major problem → new vaccines were produced and consistent
decline in hepatitis B
- Although we see an increase in frequency of mutant allele, but there wasn’t increase in
number of the infected cases.
- Possibility is that those mutant strains are outcompeted in unvaccinated hosts – cost to be
vaccine resistant
- Only ~ ¼ of the population are vaccinated
- Mutant viruses more likely to end up in people unvaccinated than vaccinated
individual→ since vaccinated individuals are rare, and most people are unvaccinated
- If the mutant virus has some cost to be vaccine resistance, it’s going to be outcompeted in
the unvaccinated host
- Mutant virus hasn’t reached the frequency to cause a wide spread
- Another possibility is that the mutant virus might have reduced the severity of the
disease. – still protection of the disease from the vaccine