HPV Vaccine During Pregnancy Does Not Increase Fetal Risk

Jennifer Garcia

March 29, 2017

Vaccination with a quadrivalent human papilloma virus (HPV) vaccine does not increase the risk for adverse outcomes during pregnancy, a new study published online March 29 in the New England Journal of Medicine shows.

"Although HPV vaccination is not recommended in pregnancy, a number of women will be inadvertently vaccinated early in the first trimester of unplanned or unrecognized pregnancies," and "data on the safety of vaccination during pregnancy are limited," write Nikolai M. Scheller, MD, from the Statens Serum Institut, Copenhagen, Denmark, and colleagues.

Using a national medical data registry, researchers in Denmark evaluated information from 540,805 women who were pregnant between October 1, 2006, and November 30, 2013. They matched vaccinated and unvaccinated women in a 1:4 ratio according to age, calendar year of pregnancy onset, and propensity score. Outcomes assessed were preterm birth, small size for gestational age, major birth defects, low birth weight, spontaneous abortion, and stillbirth. The analysis excluded women who experienced spontaneous abortion within the first 6 weeks of gestation.

In the matched analysis, exposure to the HPV vaccine did not result in a higher risk for adverse outcomes among pregnant women when compared with women not exposed to vaccine during the same time. Between the two groups, the prevalence odds ratio (OR) for major birth defects was 1.19 (95% confidence interval [CI], 0.90 - 1.58; 65/1665 exposed and 220/6660 unexposed). For preterm birth, the prevalence OR was 1.15 (95% CI, 0.93 - 1.42; 116/1774 exposed and 407/7096 unexposed).

For low birth weight, the prevalence OR was 1.10 (95% CI, 0.85 - 1.43; 76/1768 exposed and 277/7072 unexposed). For the outcome of small for gestational age, the prevalence OR was 0.86 (95% CI, 0.72 - 1.02; 171/1768 exposed and 783/7072 unexposed).

The authors demonstrated hazard ratios of 0.71 (95% CI, 0.45 - 1.14) for spontaneous abortion (20/463 exposed and 131/1852 unexposed) and 2.43 (95% CI, 0.45 - 13.21) for stillbirth (2/501 exposed and 4/2004 unexposed). The authors note, however, that because there were only two cases of stillbirth in the analysis, no clinically meaningful conclusions regarding this outcome can be drawn.

In an accompanying editorial, Kathryn M. Edwards, MD, from Vanderbilt University School of Medicine, Nashville, Tennessee, writes: "These data are very encouraging and strongly support the safety of HPV vaccines if they are inadvertently given in pregnancy, a finding that complements previous safety reports of HPV vaccine in nonpregnant women."

Noting that inadvertent vaccination of pregnant women underscores the importance of postmarketing safety evaluations, Dr Edwards writes, "The carefully conducted postlicensure safety study of HPV vaccine now reported in the Journal is a model for others to emulate."

"Our results are consistent with other evidence that does not indicate that the vaccination of pregnant women with inactivated virus, bacterial, or toxoid vaccines generally confers a higher risk of adverse pregnancy outcomes than no such vaccination," conclude Dr Scheller and colleagues.

Funding for this study was provided by the Novo Nordisk Foundation and the Danish Medical Research Council. One coauthor reports grant funding from the Novo Nordisk Foundation related to the study. One coauthor reports grant funding from the Danish Medical Research Council during the conduct of the study. Dr Edwards reports grant funding from Centers for Disease Control and Prevention, National Institutes of Health, and Novartis outside the submitted work. The remaining authors have disclosed no relevant financial relationships.

N Engl J Med. 2017;376:1223-1233. Article abstract, Editorial extract

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