Safety of influenza A (H1N1) 2009 live attenuated monovalent vaccine in pregnant women

Abstract

Objective: To characterize maternal and infant outcomes for pregnant women who received live H1N1 influenza vaccine and had no reported adverse events.

Methods: We identified Vaccine Adverse Event Reporting System reports, which described receipt of live H1N1 vaccine during pregnancy without an indication of an adverse event at the time of the report during October 2009 to June 2010. We reviewed the initial reports and obtained pregnancy outcome and infant data through 6 months of age from medical records. We reviewed the numbers and characteristics of pregnancy complications and infant outcomes including major birth defects and medically important infant conditions. Rates of spontaneous abortion, preterm birth, and major birth defects and their 95% confidence intervals were calculated.

Results: The Vaccine Adverse Event Reporting System received 113 reports stating receipt of live H1N1 vaccine during pregnancy with no adverse events reported. We obtained follow-up maternal records on 95 of the 113 (84%) live H1N1 reports (40.2% were vaccinated in the first trimester) and found: 87 live births (two twin pregnancies) and no maternal deaths occurred. Number and rates of pregnancy-specific adverse events included: 10 (10.5%, 5.8-18.3) spontaneous abortions; four (4.7%, 1.8-11.4) preterm deliveries at 35-36 weeks of gestation; three (3.4%, 1.2-9.7) infants had one or more major birth defects noted at birth: one cleft palate, one cleft lip, and one microtia (underdeveloped or absent external ear). Seven neonates and infants were hospitalized for medically important conditions. One infant death occurred in a 2.5-month-old boy as a result of pertussis.

Conclusion: Rates of spontaneous abortion, preterm birth, and major birth defects in pregnant women who received live H1N1 vaccine were similar to or lower than published background rates. No concerning patterns of medical conditions in infants were identified.

Level of evidence: : III.