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Smallpox Vaccine Virus Strain Could Determine Number of Deaths, Adverse Effects

Global Security Newswire

The strain of smallpox virus used to produce a vaccine could determine how many people suffer significant complications or die during a mass vaccination program, the New York Times reported yesterday (see GSN, Aug. 4).

A study published last month in PLos Medicine examined the rates of death and postvaccinal encephalitis — swelling of the brain — linked to a number of smallpox vaccines.

The New York City Board of Health vaccinia strain, the type stockpiled in the United States, caused 1.4 deaths per 1 million vaccinations, according to an analysis of historical records. The death rate linked to the Lister strain, maintained widely in Europe, was linked to 8.4 deaths per million. Older strains proved more deadly — the Bern strain had a death rate of 55 per million, while the Copenhagen strain was linked to 31.2 deaths per million patients.

Cases of encephalitis followed the same trend. There were 2.9 cases per million for people who received the New York strain vaccination, 26.2 with the Lister strain, 33.3 cases with the Copenhagen strain and 44.9 cases with the Bern strain.

“People in the U.S. can count themselves lucky that they live where a less pathogenic strain of vaccinia is used,” study lead author Mirjam Kretzschmar told the Times.

European nations continue to stockpile the Lister strain because its seed virus is widely available, she said.

The potential for side effects from vaccines now being developed would not be known until they are used in a mass vaccination program.

Some deaths are unavoidable in such a campaign. The researchers figured that a mass vaccination effort in the Netherlands, a country of 16 million, would cause 10 deaths using the New York strain and 55 using the Lister strain.

Smallpox itself can kill up to one-third of those who become infected (Nicholas Bakalar, New York Times, Sept. 5).