Mini Oral Australian Epidemiology Association ASM 2018

Self-Controlled Case Series Investigating the Association between Influenza Vaccination and Miscarriage (#20)

Annette K Regan 1 2 , Nicholas de Klerk 2 , Hannah Moore 2 , Gavin Pereira 1 , Paul Effler 3
  1. Curtin University, Bentley, WA, Australia
  2. Wesfarmers Centre of Vaccines and Infectious Diseases, Telethon Kids Institute, Subiaco, WA, Australia
  3. Communicable Disease Control Directorate, Department of Health WA, Perth, WA, Australia

Background: Despite national recommendations and the availability of free vaccine, just 40% of pregnant women receive inactivated influenza vaccine (IIV) each year. Safety concerns are commonly cited as a barrier, and one concern is the risk of miscarriage. Some previous studies have suggested there is an association between IIV and miscarriage, although these have been subject to bias, questioning whether IIV is associated with miscarriage.

Aim: We aimed to assess the risk of miscarriage associated with IIV during pregnancy using a self-controlled method.

Methods: Pregnancies ending in miscarriage were identified from hospital separation and emergency department (ED) presentation records in Western Australia from 2012 to 2015. Women admitted to hospital or presenting to ED with a spontaneous abortion (O03) or missed miscarriage (O02.1) were included. We used an adapted self-controlled case series which allowed for an exposure with an occurrence which may be influenced by the event. The incidence rate ratio (IRR) was estimated based on a pseudo-likelihood to compare the risk of miscarriage in the exposure period (0-28 days post-vaccination) to non-exposure periods.

Results: We identified 46 women with a pregnancy ending in miscarriage and with complete IIV exposure information; 36 women received IIV prior to eight weeks of pregnancy, 7 women between 8-12 weeks, and 3 women between 13-20 weeks. Based on a self-controlled analysis, we observed no association between IIV and risk of miscarriage (IRR: 0.99; 95% CI: 0.72-1.36).

Conclusions: These findings support the safety of vaccination during pregnancy and may support vaccine confidence.

  1. 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):5314-22.
  2. Farrington CP, Whitaker HJ, Hocine MN. Case series analysis for censored, perturbed, or curtailed post-event exposures. Biostatistics 2009;10(1):3-16.