Safety surveillance of influenza vaccine in pregnant women

Dear Editor, Pregnant women have an increased risk of influenza-related complications. Vaccination is the most effective strategy for preventing influenza infection in pregnancy. Maternal vaccination may also prevent laboratory-confirmed influenza in infants.1-3 Antenatal vaccination using trivalent influenza vaccine (TIV) is undertaken in many countries, with a recent report from the United States estimating 36.5% coverage of pregnant women in the 2011–2012 influenza season.4 The Australian Government recommends and provides free TIV for all pregnant women. However, antenatal influenza vaccine uptake in Western Australia (WA) is estimated at 6–10%,5, 6 with 61.6% of unvaccinated women concerned about the safety of vaccination during pregnancy.5 From 01 March to 31 August 2012, at least 2400 doses of TIV were administered to pregnant women in WA. A single event was reported during that time via the WA Vaccine Safety Surveillance (WAVSS) system, an online registry for health professionals and the public to report adverse events (http://www.health.wa.gov.au/vaccination/wavss.cfm). The woman (at eight weeks of gestation) reported experiencing tightness in the chest an hour following vaccination; however, symptoms resolved quickly with no medical attention sought. The Western Australian Department of Health and Vaccine Trials Group undertook a prospective vaccine safety study of TIV in pregnant women at a tertiary maternity hospital, King Edward Memorial Hospital (KEMH), in 2012. Women were contacted by telephone three to seven days following vaccination. From 01 March to 31 August 2012, 558 doses of TIV (Vaxigrip™; Sanofi-Pasteur, Lyon, France) were administered to pregnant women at KEMH with 369 (66%) contacted for follow-up. Of the 189 women who were not followed-up, 59% (112) did not provide a phone number or provided an incorrect phone number, 38% (72) were not contactable after four attempts and 3% (5) declined participation. Of the 369 women contacted, almost all (94.6%) received TIV in the second (28.2%) or third (66.4%) trimesters. Fever following vaccination was reported by 23 (6.2%) women, developing 1–48 h postvaccination (mean: 19 h) and lasting for 1–72 h (mean: 18 h). Only two women reported measuring their temperature (37.9 and 38.0 °C, respectively). Three women sought medical advice: two for fever (one of which was already in hospital when vaccinated) and one who developed sinusitis within 72 h after receiving the vaccine. Other symptoms were infrequently reported (Table 1). No convulsions were reported. Rates of reactions reported among the pregnant women surveyed were low and similar to levels reported in the Product Information for non-pregnant adults 18–59 years.7 This survey did not have sufficient statistical power to detect rare side effects; however, published data from the Vaccine Adverse Reporting System in the United States covering a 20-year period did not find any safety concerns related to the TIV among women during gestation.8 This survey was not designed to detect sequelae in infant; however, no study to date has shown an adverse consequence of inactivated influenza vaccine in pregnant women or their offspring. These data support safety of vaccination of Australian pregnant women with inactivated influenza vaccine. Ongoing surveillance is required to reassure pregnant women of the safety of TIV and drive improvements in maternal influenza coverage. We thank Caroline Talbot and other Vaccine Trial Group staff for assisting with collection of data. CB and PR are members of the Vaccine Trial Group. The Vaccine Trial Group has received funding from vaccine providers, including Sanofi Pasteur, CSL Biotherapies and GlaxoSmithKline.