H1N1 Flu Vaccine Safe for Expectant Moms, Offspring: Study

Dr. John Treanor, chief of the infectious diseases division at the University of Rochester Medical Center, in New York, said, "This is one more bit of info about the safety of vaccinations in pregnancy. There were many, many concerns at the time about potential side effects, but we didn't see them." He added, "The one thing we do have to get better at is getting it out to people early enough. We weren't ready with the vaccine in the States until the second wave of the pandemic."

Another study in the same issue of the journal found that while the risk of Guillain-Barre syndrome, a neurological condition that leads to weakness and loss of reflexes, was slightly increased after H1N1 vaccination, the risk was approximately two cases per 1 million doses.

There was significant concern when the H1N1 vaccine was in development because of an unusually high number of cases of Guillain-Barre in 1976 and 1977 following administration of the swine flu vaccine. Since that time, there hasn't been a significant risk associated with Guillain-Barre and the seasonal flu vaccine.

Between October 2009 and March 2010 in Quebec, Canada, 4.4 million people received the new H1N1 vaccine. During that time, 83 people in the whole population developed Guillain-Barre. Twenty-five of those had been vaccinated for H1N1 in the previous eight weeks, and 19 of the 25 had been vaccinated in the previous four weeks. That translated to a risk of about 2 cases of Guillain-Barre for every 1 million doses of vaccine. The risk was only seen in people older than 50, according to the study.

"In Quebec, the 2009 influenza A (H1N1) vaccine was associated with a small, but significant risk of [Guillain-Barre syndrome]. It is likely that the benefits of immunization outweigh the risks," wrote study authors Dr. Philippe De Wals of Laval University, in Quebec City, and colleagues.

Treanor said it's almost impossible to know for sure if the vaccine caused the additional cases of Guillain-Barre, but emphasized that the individual risk is "very, very small."

SOURCES: Anders Hviid, M.Sc., Dr.Med.Sci., senior investigator, Statens Serum Institut, Copenhagen; John Treanor, M.D., chief, infectious diseases division, University of Rochester Medical Center, N.Y.; July 11, 2012, Journal of the American Medical Association

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Published: July 2012