Reply #4: Smallpox immunity may last a lifetime

[RC]

http://www.newscientist.com/news/news.jsp?id=Ns99994064

Vaccination may induce life-long immunity to smallpox, suggest the results of the first detailed tests of their kind. This means that any terrorist release of smallpox might not spread as catastrophically fast as feared, and fewer people might die.

Smallpox was declared eradicated in the wild in 1980, after a worldwide vaccination campaign. But the disease stopped circulating earlier in the west, and routine vaccination ceased in the 1970s. That means most westerners born since then have not been vaccinated, making smallpox - which is highly contagious and kills a third of its victims - potentially a horrific biological weapon.

But how horrific depends on whether people who were vaccinated have retained their immunity. It has been assumed that few would.

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Taken together with the earlier observations, "this suggests that long-term smallpox immunity might depend on antibodies, not T-cells," says Slifka. This would be good news, because in the test group antibodies seemed to remain "remarkably stable" after vaccination.

It suggests that half of those vaccinated as children - about one in four westerners - is currently immune to smallpox. Furthermore, nearly all of the rest of the vaccinated population may be partially immune. This could mean they might get only mild disease, says Slifka, and - importantly for control measures - would probably not be contagious.

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Study: Smallpox immunity remains in body for years after vaccination

http://www.vaccinationnews.com/DailyNews/2003/May/22/StudySmallpox22.htm

People vaccinated against smallpox as long as 75 years ago may still retain some immunity to the disease, a new study finds. That means as many as 150 million Americans could already be significantly protected, researchers say.

Antibodies to vaccinia, the live virus used in the smallpox vaccine, were present in more than 90% of the 306 people tested, and remained fairly constant whether the participants were vaccinated a year ago or as far back as 1928, says researcher Mark K. Slifka of the Oregon Health and Science University. "From one to 75 years out, the levels were in the same range," he says.

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Check the dates. The newer studies say that the immunity remains. Studies older than two years old it doesn't. I am old enough to remember when it was common knowledge that getting it once conferred lifetime immunity.