Following the publication of a study suggesting that pregnant women who had a spontaneous abortion were more to have received the inactivated pandemic H1N1 (H1N1pdm09) antigen influenza vaccine in the previous 28 days, the US Centers for Disease Control and Prevention (CDC) has released updated guidance regarding the use of the influenza vaccine in pregnant women.1
The CDC-funded study, published in Vaccine,2 found an increased risk of spontaneous abortion in pregnant women 28 days after vaccination. These women (n=485) were vaccinated in both the 2010-2011 and 2011-2012 flu seasons with vaccines containing H1N1pdm09. James G. Donahue, PhD, MPH, of Marshfield Clinic Research Institute in Wisconsin, and colleagues, conducted the case-control study. Adjusted odds ratio (aOR) for experiencing spontaneous abortion during the 28-day exposure window was 2.0 (95% CI, 1.1-3.6); aOR in season-specific analyses were 3.7 and 1.4 (95% CI 1.4-9.4 and 0.6-3.3 in 2010-2011 and 2011-2012, respectively).
Dr Donahue and colleagues concluded that “[t]he association was significant only among women vaccinated in the previous influenza season with pH1N1-containing vaccine. This study does not and cannot establish a causal relationship between repeated influenza vaccination and [spontaneous abortion].”
In the latest guidance, the CDC and the Advisory Committee on Immunization Practices (ACIP) noted that they have not changed the standing recommendation for influenza immunization in pregnant women.2 They stated, “It is recommended that pregnant women get a flu vaccine during any trimester of their pregnancy,” due to the danger that influenza can pose to pregnant women.
The CDC is currently conducting an ongoing study of pregnant woman who were eligible to receive influenza vaccinations during the 2012-2013 and 2014-2015 flu season, and anticipate results in late 2018 or 2019.
- Flu vaccination & possible safety signal. Information and guidance for health care providers. Atlanta, GA: US Centers for Disease Control and Prevention. www.cdc.gov/flu/professionals/vaccination/vaccination-possible-safety-signal.html. Updated September 13, 2017. Accessed September 18, 2017.
- Donahue JG, Kieke BA, King JP, et al. Association of spontaneous abortion with receipt of inactivated influenza vaccine containing H1N1pdm09 in 2010-11 and 2011-12. Vaccine. 2017;35(40):5314-5322.