Risk of Fetal Death after Pandemic Influenza Virus Infection or Vaccination

Abstract

Background During the 2009 influenza pandemic, pregnant women were at particular risk of serious influenza illness. This concern was further complicated by questions about vaccine safety in pregnant women raised by anecdotal reports of fetal deaths following vaccination. Methods We explored the safety of influenza vaccination of pregnant women by linking Norwegian national registries and medical consultation data to determine influenza diagnosis, vaccination status, birth outcomes, and background information for pregnant women before, during, and after the pandemic. We used Cox regression models to estimate hazard ratios of fetal death, with gestational day as the time metric and vaccination and pandemic exposure as time-dependent exposure variables. Results There were 117,347 eligible pregnancies in Norway in 2009–2010. Fetal mortality was 4.9/1000. 54% of pregnant women in their second or third trimester during the pandemic were vaccinated. Vaccination in pregnancy substantially reduced the risk of influenza diagnosis (adjusted hazard ratio, 0.30; 95% confidence interval [CI], 0.25 to 0.34). A clinical diagnosis of influenza in the mother increased the risk of fetal death (adjusted hazard ratio, 1.91; 95% CI, 1.07 to 3.41). Among pregnant women, the risk of fetal death was lower with vaccination, although this reduction was not statistically significant (adjusted hazard ratio, 0.88; 95% CI, 0.66 to 1.17). Conclusions Pandemic influenza in pregnancy was associated with increased risk of fetal death. Vaccination during pregnancy reduced the risk of influenza diagnosis. Vaccination itself did not increase fetal mortality, and may have reduced the risk of influenza-related fetal death during the pandemic.

Risk of Guillain-Barré syndrome after exposure to pandemic influenza A(H1N1)pdm09 vaccination or infection: a Norwegian population-based cohort study

“…The pandemic peak in Norway occurred between October 1, and December 31, 2009 [18]. The vaccination campaign began on October 19, 2009, and about 97 % of the pandemic vaccinations were administered before December 31, 2009.…”

Protective Role of Passively Transferred Maternal Cytokines against Bordetella pertussis Infection in Newborn Piglets

“…Vulnerability of this group most recently has been stressed with the higher mortality from pandemic H1N1 influenza in pregnant women and fetuses than in the general population (8,9). Universal administration of tetanus toxoid (TT) during pregnancy is the best example of how this approach can be effectively utilized (10,11).…”

Maternal immunization

“…Multiple studies document the immunogenicity [27][28][29] and safety 30,31 of maternal influenza vaccination. Studies of seasonal 32 and pandemic 33,34 influenza vaccination in the United States and abroad suggest that exposure to the influenza vaccine during pregnancy does not appear to be associated with obstetric or fetal complications. [35][36][37][38] In fact, maternal immunization may reduce rates of preterm birth and suboptimal growth among infants of vaccinated mothers.…”

“…67,87 Reassuringly, patients' focus on potential vaccine harm comes at a time of growing data about the benefits and safety of maternal vaccination for babies. 32,33,35,[39][40][41] Emphasizing the benefits of maternal immunization, including its safety and absence of fetal harm, should help decrease the perceived cost of maternal immunizations.…”