Surveillance of Adverse Events After Seasonal Influenza Vaccination in Pregnant Women and Their Infants in the Vaccine Adverse Event Reporting System, July 2010-May 2016.
Level 4 - case-series / case-control
Passive surveillance case series without an unexposed comparator group
PubMed 27988883 · doi:10.1007/s40264-016-0482-1
What was done
Researchers searched the US Vaccine Adverse Event Reporting System (VAERS) for adverse event reports in pregnant women who received seasonal inactivated influenza vaccines (IIV) or live attenuated influenza vaccines (LAIV) between July 1, 2010, and May 6, 2016. Clinicians reviewed reports and available medical records, assigned primary clinical categories, and coded reports as serious based on Code of Federal Regulations definitions.
What was found
Of 671 total reports identified, 544 followed IIV and 127 followed LAIV. Serious adverse events occurred in 61 (11.2%) IIV reports and 1 (0.8%) LAIV report, with zero maternal deaths. Among 296 reports specifying gestational timing, IIV was administered during the first trimester in 116 (39.2%). Among IIV reports, the most frequent pregnancy-specific adverse events were spontaneous abortion in 62 (11.4%) reports, stillbirth in 10 (1.8%), and preterm delivery in 6 (1.1%). The most common non-pregnancy-specific adverse event was injection-site reactions in 55 (10.1%) reports. Neonatal or infant outcomes were noted in 22 (4.0%) reports, including 7 with major birth defects of different types and zero neonatal deaths.
Why it matters
This surveillance study reinforces the post-licensure safety profile of seasonal influenza vaccines in pregnancy, demonstrating no new or unexpected maternal, fetal, or infant adverse outcome patterns.
Limits
VAERS is a passive surveillance database subject to underreporting, reporting bias, and variable data completeness. The study design lacks an unexposed comparison group, cannot establish causality or calculate true incidence rates, and lacked gestational trimester information for over half (375 of 671) of the reports.
Cited by
- supports A December 2016 published study on adverse events after seasonal influenza vaccination in pregnant women found that the 2009 spike in VAERS reports was attributable to stimulated reporting rather than true increases in adverse outcomes.