The duration of the protective effects induced by vaccination against smallpox with the standard vaccinia was unknown. Now, in a letter to August 29
Frelinger & Garba tested the CD8+ T-lymphocyte responses to vaccinia virus in people who had been recently vaccinated (within five years), unvaccinated people, and those who had been vaccinated 6 to 35 years earlier or more than 35 years earlier. They observed that the loss of CD8+ T-lymphocyte response over a period of more than 35 years was very low — by a factor of less than two in all nine people with a remote history of vaccination (4% of CD8+ T lymphocytes), as compared with the recently vaccinated (6.5%...
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