President George Bush announced last week that a million Americans will be vaccinated against smallpox by early 2003. But the precaution will be costly: the contagious vaccine will sicken and almost certainly kill a few people. The only tested remedy is in short supply and may not work for all adverse reactions.
The smallpox vaccine will first be given to half a million US troops and a similar number of health workers. It will then be offered to up to 10 million more health and emergency workers.
The vaccine consists of live vaccinia virus. In some people it can cause inflammation of the brain, death of the skin around the vaccination site or a severe form of eczema. And vaccinated people can infect others for up to three weeks afterwards.
Two studies in the 1960s found that there were "life-threatening" reactions in between 14 and 52 people per million vaccinated, and one or two per million died. The side effects now will almost certainly be more severe. Recently, Israel vaccinated 1500 healthcare workers, and one suffered serious side effects. The numbers are too small to draw any firm conclusions, but it is hardly encouraging.
What's more, unlike most Americans, the Israeli group had all been vaccinated before, so they should have had a lower risk of reacting adversely. Israel also uses the Lister vaccine, which causes fewer adverse reactions than the US strain.
Another cause for concern is that there are now many people with suppressed immunity, due to HIV or therapy for cancer or transplants. There were none in the 1960s. They will be excluded from vaccination along with around 50 million Americans who once had eczema or topical dermatitis, which can increase the risk.
The danger is that these high-risk groups could catch vaccinia from those vaccinated. An immunosuppressed Israeli, who lived with a vaccinee, is reported to have fallen seriously ill. Even in the 1960s, when most people were immune to vaccinia, about 30 people caught vaccinia per million people vaccinated. Now even those vaccinated as children may not still be immune- yet there are no plans to isolate vaccinated health workers from patients.
The one treatment for serious complications is vaccinia immune globulin (VIG) - antibodies harvested from vaccinated people. Yet until recently the only VIG in the US dated from 1995, and was no longer approved for use as it had become discoloured. The authorities now say they will have 2700 fresh doses prepared by next month. No one knows if that will be enough and it is not recommended for brain inflammation, which can be lethal. There is also the antiviral drug cidofovir, but no one knows if it will work.
New Scientist issue: 21/28th December 2002
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