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H1N1 vaccine given to pregnant women not linked to poor birth outcomes
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Two separate studies published this week had somewhat contrasting findings regarding the safety of influenza A(H1N1) vaccine.
The 2009 pandemic influenza vaccine appeared to slightly increase the risk for Guillain-Barre syndrome among adults, but the vaccine was not associated with preterm birth or birth defects when given to pregnant women, according to two studies published online in the Journal of the American Medical Association.
Guillain-Barre syndrome
In the first study, Philippe De Wals, MD, PhD, of Laval University, Quebec City, Canada, and colleagues assessed the risk of GBS following pandemic influenza vaccination in the fall of 2009 through March 2010.
During the 6-month period, the researchers noted 83 confirmed GBS cases. Twenty-five patients with confirmed GBS had been vaccinated against 2009 influenza A (H1N1) 8 or fewer weeks before disease onset, with most (19/25) vaccinated 4 or fewer weeks before onset. Analysis of data indicated “a small but significant risk of GBS following influenza A(H1N1) vaccination.”
The number of cases attributable to vaccination was approximately 2 per 1 million doses. The excess risk was observed only in patients aged 50 years or older, according to the study findings.
“In Quebec, the individual risk of hospitalization following a documented influenza A(H1N1) infection was 1 per 2,500 and the risk of death was 1/73,000. The H1N1 vaccine was very effective in preventing infections and complications. It is likely that the benefits of immunization outweigh the risks,” the authors wrote.
Birth defects
In the second study, Björn Pasternak, MD, PhD, of the Statens Serum Institut, Copenhagen, Denmark, and colleagues looked at data from a registry-based study that included all live-born singleton infants in Denmark delivered between Nov. 2, 2009, and Sept. 30, 2010. The researchers estimated the prevalence odds ratios of adverse fetal outcomes, comparing infants exposed and unexposed to an AS03-adjuvanted influenza A (H1N1)pdm09 vaccine during pregnancy. Following exclusions, a cohort of 53,432 live-born infants was identified with 6,989 (13.1%) exposed to the vaccine during pregnancy.
In a propensity score-matched analysis of 330 infants exposed to the vaccine in the first trimester of pregnancy and 330 unexposed, there were 18 infants diagnosed with a major birth defect among those exposed compared with 15 among the unexposed. Among infants exposed to the H1N1 vaccine in the first trimester, 31 were born preterm compared with 24 among the unexposed. Preterm birth occurred in 302 of 6,543 infants with second- or third-trimester exposure, compared with 295 of 6,366 unexposed infants.
In an accompanying editorial written by Mark C. Steinoff, MD, and Noni E. McDonald, MD, MSc, the authors mention how these studies mostly alleviate concern about safety of adjuvanted pandemic vaccines during pregnancy; however, they encourage more studies of pandemic influenza vaccines during pregnancy and vaccine adjuvants.
Disclosure: The first study was funded by the Ministere de la Sante et des Services sociaux du Quebec and by the Public Health Agency of Canada-Canadian Institutes for Health Research Influenza Research Network. The second study was funded by the Danish Medical Research Council. No researcher reported any conflicts of interest.
For more information:
- De Wals P. JAMA. 2012;308[2]:175-181
- Pasternak B. JAMA. 2012;308[2]:165-174.
Perspective
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Pedro A. Piedra, MD
Influenza vaccine is recommended annually to all everyone aged 6 months and older in the United States. In 2005, the trivalent inactivated influenza vaccine (TIV) was recommended to pregnant women during any trimester by the Advisory Committee on Immunization Practices of the CDC and the American College of Obstetricians and Gynecologists. Pregnant women are at higher risk of influenza-associated death and hospitalization compared to non-pregnant women of child-bearing age.
During the 2009 influenza A(H1N1) pandemic, substantial morbidity and mortality was observed in pregnant women. Influenza vaccination coverage of pregnant women in the United States was very low (~15% or lower) prior to the 2009 pandemic. Low coverage was due, in part, to unfounded safety concerns to the fetus and the pregnant women. The recommendation by advisory boards around the world to vaccinate pregnant women against the 2009 influenza A(H1N1) pandemic virus provided additional opportunities to report on the safety of TIV in this vulnerable population. The registry-based cohort study by Pasternak and colleagues (JAMA. 2012:308:165) reported on the safety of the AS03-adjuvanted influenza A(H1N1) pandemic vaccine in pregnancy. The authors utilized the Danish registry of live-born infants and linked it to individual data on influenza vaccination of pregnant women and their potential confounders. Unmatched and propensity score-matched cohorts of infants born to mothers who received or did not received AS03-adjuvanted influenza A(H1N1) pandemic vaccine were analyzed to determine prevalence odd-ratio of adverse fetal outcomes.
Overall, the AS03-adjuvanted influenza A(H1N1) pandemic vaccine was safe in women during any trimester of pregnancy and was not associated with an increased risk of major birth defects, prematurity or decrease fetal growth. A novel contribution by Pasternak and colleagues was the demonstration that the AS03 adjuvant in combination with the TIV was safe during pregnancy.
In the United States, all the FDA approved TIV do not contain an adjuvant. In Europe, both adjuvanted and non-adjuvanted TIV are used. It is possible that in the near future. an adjuvanted TIV will be approved for the US market.
This report is reassuring and adds to excellent safety profile of IIV during pregnancy.
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