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Study Affirms Low Risk of Virus in Blood Donated by Smallpox Vaccine Recipients

Current blood donation guidelines for individuals who have been vaccinated against smallpox with live vaccinia virus (Dryvax) are likely sufficient to protect recipients of that blood from vaccinia infection, according to new confirmatory findings.

NIAID researchers, in collaboration with their colleagues at the National Institutes of Health Clinical Center, found rare instances of vaccinia virus DNA—but not infectious virus—in blood samples taken from 28 NIH employees who had received the Dryvax smallpox vaccine as recommended for their jobs.

Using two different testing methods for blood samples, the research team found only four out of 200 specimens tested positive for vaccinia virus DNA. Moreover, the positive results were deemed “weakly positive” and samples did not contain detectable infectious virus. In addition, no vaccinia virus DNA or infectious virus was detected in throat swabs.

The findings are contrary to the conclusions of an earlier study that recommended extending the time between when individuals are vaccinated against smallpox and when those people can donate blood.

“Like the earlier study, we also found evidence of the smallpox vaccine virus DNA in the blood,” says lead researcher Jeffrey I. Cohen, M.D., chief of the Medical Virology Section in the NIAID Laboratory of Clinical Infectious Diseases. “However, the earlier study did not look for infectious virus in the blood. We were able to look at the same samples that were positive for viral DNA and found no infectious virus. Thus, we feel that as long as the current guidelines for donating blood after smallpox vaccination are followed, the risk of transmitting the vaccine virus through blood transfusions should be exceedingly small.”

The current guidelines recommend that Dryvax recipients who do not develop complications from vaccination should defer from donating blood until after the vaccine scab has spontaneously separated or after 21 days, whichever is longer. Individuals with vaccine complications, the guidelines advise, should defer from donating blood until 14 days after all complications cease.

Reference

JI Cohen et al. Detection of vaccinia virus DNA, but not infectious virus, in the blood of smallpox vaccine recipients. Vaccine 25(23): 4571-74 DOI: 10.1016/j.vaccine.2007.03.044 (2007).

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Last Updated August 30, 2007