The duration of the protective effects induced by vaccination against smallpox with the standard vaccinia was unknown. Now, in a letter to August 29 New England Journal of Medicine, Jeffrey Frelinger and Mohammed Garba from the University of North Carolina, US point out that responses to smallpox vaccine do not diminish in time and may offer long lasting benefits.

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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