- If you had a smallpox vaccination as a child and think
you are still protected, think again - almost everyone vaccinated before
smallpox was eradicated in the mid-1970s has now lost their immunity.
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- The bad news comes from a study of 621 microbiologists
in Maryland who received fresh vaccinations between 1994 and 2001 to protect
them in their work. Only about 40, or just six per cent, were still immune
from their earlier vaccinations.
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- "The study is, to the best of my knowledge, the
only one since eradication which tries to look at the durability of immunity,"
says lead author Michael Sauri, director of the Occupational Medicine Clinic
in Maryland. "It's showing us that after 20 years immunity is not
going to be there."
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- In the US, for example, about 60 per cent of the population
has had a smallpox vaccination. The study suggests that most of these people
are now just as susceptible to smallpox as the 120 million born since the
government halted vaccination in 1972.
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- That strengthens the case for pre-emptive immunisation,
some experts think. "It adds to the argument that you can't count
on any protection we thought we had," says Bill Bicknell of Boston
University, a former commissioner of the Massachusetts Department of Public
Health who has been arguing for mass vaccination since the anthrax attacks,
in case terrorists try smallpox next.
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- Deaths from complications
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- Bicknell thinks that outbreaks would be much easier to
contain if almost everyone is vaccinated. "I'm not saying you just
go straight in and vaccinate the population - you'd do it steadily in stages,"
he says. Healthcare workers would be first, followed by volunteers screened
to check they are healthy.
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- But extrapolating from figures from the last mass vaccination
in 1968 suggests at least 180 people would die of complications. That's
a high price to pay for protection against an attack that may never happen.
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- The Centers for Disease Control in Atlanta believes mass
vaccination is unnecessary and it can deal with an outbreak through "ring
vaccination" of people in the affected zone, plus their contacts.
It says its contingency plans for dealing with a smallpox outbreak, which
will be reviewed this month, assume that no one is immune anyway.
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- In Britain, where smallpox vaccination stopped in 1980,
the Department of Health is taking the same approach. "We won't be
relying on any current immunity of the population," says a spokesman.
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- Long-life antibodies
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- Nevertheless, Harold Margolis, the CDC's chief adviser
on smallpox preparedness, remains convinced that there are higher levels
of immunity in the general population than the study suggests. "We
don't know a lot about the determinants of long-term immunity," he
says.
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- Previous studies earlier this century in England and
in the US suggested that immunity could last 50 years or more, Margolis
says. "It won't protect you against infection, but it might protect
you from death."
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- He also pins hopes on a 1990 Israeli study showing that
antibodies against the virus last for decades.
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- Journal reference: Maryland Medicine (Spring 2002 issue,
p 44)
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- http://www.newscientist.com/news/news.jsp?id=ns99992338
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