| Contrary to popular belief, the smallpox vaccination can last up to 30 years or longer, according to a US study to be published on Thursday in the New England Journal of Medicine.
"Given the general belief that the vaccinations lasted only seven to 10 years, we were surprised how durable the responses were," said study co-author Jeffrey Frelinger, professor and chairman of microbiology and immunology in the School of Medicine.
Loss of reactivity low
Frelinger and his postdoctoral researcher Lawal Garba from the University of North Carolina at Chapel Hill noted "two observations are obvious, vaccinia induces a robust CD8 T lymphocyte response in healthy individuals and, second, the response is of long duration."
Their tests showed that people who had been immunised decades earlier still reacted to the vaccine by producing interferon-gamma, proteins produced by T cells when responding to an attack on the immune system.
"It is striking that the loss of reactivity over more than 35 years is very low in individuals with a remote history of vaccination compared to recently vaccinated individuals," they said.
A healthy 4.8 percent of CD8 cells in people vaccinated more than 35 years ago responded to the vaccinia, versus 6.5 percent in people recently vaccinated.
Changing immunisation policy
According to Frelinger, the discovery of the long-lasting benefits of the immunisation could influence US smallpox vaccination strategies envisioned by medical experts in case of a smallpox bioterrorist attack.
"If you had a limited supply of vaccine, I think you'd want to target predominantly previously unvaccinated individuals," he said, underlining the importance of immunising people who have never been immunised against the disease, which was declared eradicated in 1980. – (Sapa-AFP)
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