Smallpox vaccine protection may last a few decades

NEW YORK, Sep 20 (Reuters) Most patients are fully protected against smallpox for a few decades after primary smallpox vaccination and protection against severe disease for up to 50 years, according to a new report.

''Median duration of protection against the disease would be more or less 20-30 years,'' Dr. Martin Eichner from University of Tuebingen, Germany told Reuters Health.

''In other words, the present population may not be protected against infection unless recently vaccinated. However, some fraction of previously vaccinated individuals may still be protected against the severe forms of the disease.'' Smallpox killed millions of people each year into the 1960s and left many more blind and scarred. Smallpox was officially eradicated in 1979 after a worldwide vaccination campaign.

Eichner and colleagues used data from the smallpox outbreaks before and after 1900 in the UK to estimate the duration of protection provided by vaccination against smallpox.

Based on these data, the median protection during major smallpox outbreaks ranged from 11.7 to 28.4 years after primary vaccination.

As late as 50 years after primary vaccination, as many as 78.8 per cent of vaccinated individuals were still protected against the severe manifestations of smallpox, and severe cases were extremely rare within 20 years of vaccination.

''We should pessimistically assume that previously vaccinated individuals are no longer protected against the infection, but many of those who have been vaccinated may still possess partial protection against the severe forms of the disease,'' Eichner said.

''Although this certainly is good news for an afflicted individual, we still do not know whether such partial protection will work out positively or negatively on the population level in the event of a bioterrorist attack.'' ''Transferring these historical data to a modern situation, we have to be very careful,'' Eichner cautioned. ''The vaccine which was used has constantly changed, and all of us have certainly received a vaccine which must have differed from those a hundred years or so ago. One may also hope that the modern vaccines were even more potent than the old ones,'' he added.

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