TUESDAY, July 10 (HealthDay News) -- Exposure to adjuvanted influenza A(H1N1)pdm09 vaccination during pregnancy does not increase the risk of adverse fetal outcomes, and influenza vaccination correlates with a small but significantly increased risk of Guillain-Barré Syndrome (GBS), according to two studies published in the July 11 issue of the Journal of the American Medical Association.
Björn Pasternak, M.D., Ph.D., from the Statens Serum Institut in Copenhagen, Denmark, and colleagues examined the risk of adverse fetal outcomes for infants exposed to an adjuvanted influenza A(H1N1)pdm09 vaccine during pregnancy in propensity score-matched analyses of a Danish cohort. The researchers found that there was no significantly increased risk of a major birth defect for infants exposed in the first trimester versus unexposed infants. There was also no increased risk for preterm birth or small for gestational age for those exposed in the first trimester, or the second or third trimesters, versus unexposed infants.
Philippe De Wals, Ph.D., from the Université Laval in Québec, and colleagues examined the risk of GBS after pandemic influenza A(H1N1) vaccine administration in Québec in 2009. The researchers identified 83 cases of GBS over a six-month period, 25 of which had been vaccinated eight or fewer weeks before disease onset. In the eight-week postvaccination period, the age- and sex-adjusted relative risk was 1.80 for all confirmed cases and, in the four-week postvaccination period, the relative risk was 2.75. Per one million doses, approximately two cases of GBS were attributable to vaccination.
"In Québec, the 2009 influenza A(H1N1) vaccine was associated with a small but significant risk of GBS," De Wals and colleagues conclude. "It is likely that the benefits of immunization outweigh the risks."
Several authors from the de Wals study disclosed financial ties to the pharmaceutical industry.
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