Doubts over UK smallpox vaccine dismissed


By Debora MacKenzie The smallpox vaccines ordered by the UK and the US are likely to be equally effective – or, possibly, they may be equally ineffective. Reports that the strain of smallpox vaccine now being stockpiled by the UK will not work, while the US stockpiled vaccine will, are wrong, according to smallpox experts. But New Scientist can also reveal that neither is certain to work. This is because the old tried-and-tested vaccines, which eradicated smallpox, were made on the skin of live animals and the new ones will not be. The US currently has a stockpile of 165 million doses of the old-style smallpox vaccine. But because of fears following the events of September 11 that terrorists may possess smallpox, the US decided to order an extra 55 million doses of new vaccine a year from the UK-based firm Acambis. In April 2001, the UK followed suit by ordering an undisclosed number of doses of new vaccine from the British firm PowderJect, to add to its three million dose stockpile of old vaccine. The UK contract had already been criticised by opponents of the UK’s governing Labour Party, because PowderJect CEO Paul Drayson has donated money to Labour. But on Tuesday, allegations surfaced in the UK press that the choice was not even medically warranted, as the UK vaccine will be derived from the Lister strain, while the US will use a strain named after the New York City Board of Health. The charge is that Lister will not protect against an especially virulent strain of smallpox, India-1967, which was weaponised by the tonne under the old Soviet bioweapons programme. It is feared that this strain is most likely to have fallen into unfriendly hands. The NYCBH strain probably does work against India-1967, as a Soviet derivative of it was widely used during the smallpox eradication campaign in India. “But Lister vaccines were used very widely in India, and they worked” says Ian Simpson of the World Health Organization. In fact, Lister was the most widely used smallpox vaccine in the world, according to the WHO, which supplied the strain to vaccine manufacturers. The WHO advised either strain could be used in the eradication programme. But all that may have little to do with the vaccines being made now. The old vaccines were made by infecting animals with the Vaccinia virus, a smallpox-relative, and then scraping infected material off pustules on their skin. That is no longer an acceptable production method, because of the possibility of contamination with other pathogens. Both Acambis and PowerJect will be making their vaccines under sterile conditions in large cultures of cells. However, the European Agency for the Evaluation of Medicinal Products (EMEA), the EU’s governing body for pharmaceuticals, warns in a June report: “There is little or no experience of the effectiveness of cell culture grown vaccines against smallpox.” It notes that production using tissue cultures would select for strains of the virus that thrive in those cells, meaning that the final strain emerging from intensive cell culture may bear little comparison to its parents. The EMEA warns that the effect of this on the efficacy and safety of the vaccine needs to be studied. The effect might be so large compared to differences in the parent strains that the EMEA felt it could not choose between either Lister or NYCBH as the parent strain of choice. Simpson cautions that “there is no reason to think tissue-culture produced vaccines will necessarily be less effective than the old vaccines”. It is simply not known. Safety studies are underway for the Acambis vaccine, but there is no way to test either vaccine’s effectiveness at protecting humans – smallpox has been eradicated. EMEA recommends tests in animals using related pox diseases, and measuring antibodies after vaccinating humans,
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