Influenza vaccination bears no increased risk of adverse birth outcomes

Influenza vaccination of pregnant women has no negative effect on the foetus, regardless of the trimester in which the shot is given, a study from Japan has found.

The study population comprised 10,330 pregnant women, among whom 3,943 (38 percent) were vaccinated and 6,387 (62 percent) were not. Vaccinated women were older and more commonly had underlying obstetric and gynaecological illnesses. On the other hand, unvaccinated women (control) frequently smoked or drank alcohol during pregnancy and were more likely to have obesity, hypertension, or foetal growth restriction as pregnancy-induced complications.

Researchers followed all women until the end of their pregnancy. They assessed the safety of vaccination in terms of adverse birth outcomes, including miscarriage, stillbirth, preterm birth, low birth weight and malformation.

The incidence of adverse birth outcomes did not significantly differ between the vaccinated and control groups (9 percent vs 10 percent, respectively). Multivariable logistic regression analysis confirmed that vaccination during pregnancy conferred no increase in the risk of adverse birth outcomes (odds ratio [OR], 0.90, 95 percent confidence interval [CI], 0.76–1.07).

Moreover, timing of vaccination did not alter the findings. Vaccination during the first or second trimester was not association with adverse birth outcomes, whereas administration of the vaccine during the third trimester even exerted a protective effect on the risk (OR, 0.70, 95 percent CI, 0.51–0.98).

Despite the presence of several limitations, the present data should help allay concerns regarding the effect of influenza vaccination on the foetus, the researchers said.