December 6, 2011 — A single dose of a monovalent, nonadjuvanted 2009 influenza A(H1N1) vaccine conferred seroprotection to pregnant women and neonates, according to the findings of a phase 2, prospective, single-group clinical trial.
Vassilis Tsatsaris, MD, PhD, from the CIC de Vaccinologie Cochin-Pasteur, in Paris, France, and colleagues published their findings in the December 6 issue of the Annals of Internal Medicine.
The authors note that pregnant women are at a disproportionate risk for adverse outcomes regarding 2009 influenza A(H1N1) infection. "A CDC survey confirmed [the] disproportionate risk for death from 2009 influenza A(H1N1) in pregnant women, which led to their designation as a top-priority group to receive the 2009 H1N1 vaccine," the authors write. "French authorities recommended vaccination with a single dose of a nonadjuvanted H1N1 vaccine for all pregnant women after the first trimester."
The study population consisted of 110 pregnant women between 18 and 45 years of age and between 220/7 and 320/7 weeks of gestation, of whom 107 were vaccinated and included in the data analysis. Among the 107 eligible women, investigators observed hemagglutination inhibition antibody titers of 1:40 or greater in 98% (95% confidence interval [CI], 93% - 100%) of the women on day 21 after vaccination, with a seroconversion rate (≥4-fold improvement in antibody titers after vaccination compared with those before vaccination) of 93% (95% CI, 86% - 97%).
The researchers noted hemagglutination inhibition antibody titers of 1:40 or greater in 95% (95% CI, 89% - 99%) of cord serum samples.
The authors excluded women who were allergic to components of the vaccine, had a severe reaction to previous H1N1 vaccination, or were previously vaccinated in the 3 weeks before enrollment were excluded. Moreover, the authors excluded women with any number of health conditions, including heart or liver disease, multiple sclerosis, and diabetes before pregnancy.
At 21 and 42 days after vaccination and at delivery, 100% (95% CI, 96% - 100%), 100% (95% CI, 97% - 100%), and 99% (95% CI, 95% - 100%) of women exhibited neutralizing antibody titers against the A/California/7/2007(H1N1v) strain of 1:40 or greater. In addition, 98% (95% CI, 92% - 100%) of cord serum samples exhibited neutralizing antibody titers of 1:40 or greater.
Daniel Floret, MD, from Hospices Civils de Lyon in France, commented about the importance of demonstrating the efficacy of the nonadjuvanted vaccine. "France was the first country in Europe to decide not to use adjuvanted vaccine to immunize pregnant women," Dr. Floret told Medscape Medical News. "It was important to prove that such a vaccine could protect the infants." Dr. Floret was not involved in the study.
Dr. Tsatsaris has board membership at Ferring, and his institution has received grants from Beckman, Ferring, and Aloka. Dr. Tsatsaris also has been paid for lectures by Ferring and Beckman. One of the coauthors is a consultant for Sanofi Pasteur MSD and has received payment for lectures from Sanofi Pasteur MSD. The remaining authors and commentators have disclosed no relevant financial relationships.
Ann Intern Med. 2011;155:733-741. Abstract
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