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Friday, October 26, 2018

Comments

Sawyer

Why did vaccine use to be useless?

edmund

'Useless' is obviously a bit sweeping. Vaccine efficacy is judged by comparing the attack rate- i.e. people who get the target disease -in vaccinated people or groups versus the attack rate in non-vaccinated. Measles vaccine is at the top of the range - about 95% protective efficacy. Typhoid is much lower (don't know the exact number).
As to why measles vaccine is effective and the old typhoid vaccine much less so: I don't really know but the most likely is that the vaccine simply didn't provoke enough antibody response in recipients.
Some vaccines (e.g. influenza and malaria) lack efficacy because the target keeps changing but I don't think that applies to typhoid.

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