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Smallpox vaccines

New Scientist

THE claim that Britain's smallpox vaccine is less likely to protect people in the event of a bioterrorist attack than the US version sparked a political row last week. But the US government's top adviser on smallpox has told New Scientist that they are both equally likely to work.

The claim that the British vaccine is inferior was made by Stephen Prior of the Potomac Institute for Policy Studies. He looked at which vaccines were used where, and with what success, during the eradication programmes of the 1960s and 1970s.

Two vaccines were used widely during this time. One was developed by the Lister Institute in Britain, the other by the New York City Board of Health. Last year, as fears grew that terrorists would try a smallpox attack, the US ordered the NYCBH strain from a company called Acambis. This April, Britain ordered the Lister strain from another company, PowderJect.

The British government is already under fire for awarding the contract to PowderJect without putting it out to competitive tender, especially as the head of the company has made contributions to the governing Labour Party. So the media seized on Prior's charges that PowderJect's vaccine may not protect against the smallpox strain most likely to be used by terrorists: India-1967, which was mass-produced by the Soviet Union.

Prior says the Lister strain was used later in the eradication drive, in places where the virus was no longer in circulation, whereas the NYCBH strain was more widely used where smallpox was still endemic, especially in India, where India-1967 was probably circulating. "It would therefore seem logical to have any vaccine-based defence [use] the vaccine strains that exhibited success during the eradication campaign," he concludes.

But DA Henderson of Johns Hopkins University, who led the smallpox eradication drive and is the US's chief smallpox adviser, rejects Prior's claims. He says the Lister strain was used to eliminate the virus in countries where it was still circulating, including Indonesia, Bangladesh, Nepal, Pakistan and Kenya. Even India used it successfully in areas where the virus was still endemic. "The Lister strain, so far as we could tell, was fully as protective as the New York Board of Health strain," Henderson says.

Indeed, none of the smallpox experts contacted by New Scientist think Prior's claim stands up. But that doesn't mean there's nothing to worry about. For one thing, it's not clear whether Britain will have enough vaccine to contain an outbreak, as the government won't disclose how many doses it has ordered from PowderJect. By contrast, the US plans to stockpile enough for its entire population.

What's more, both vaccines are being made by an untested method. In the past, they were made by scraping virus-laden material from pustules on the skin of infected animals. Now they will be harvested from cells grown in culture. But in June, the European Agency for the Evaluation of Medicinal Products, warned that growing the virus in cell culture will select for particular variants that may- or may not- be as effective at protecting against smallpox.

There is no way to test this directly. But so far, says Henderson, indirect studies suggest that cultured NYCBH vaccine is the same as the original.

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Author: Debora MacKenzie,

New Scientist issue: 10 AUGUST 2002

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