Researchers found the acellular pertussis (Tdap) vaccine was not linked to preterm birth or small-for-gestational-age birth when given to pregnant women.
The vaccine was licensed in 2005 for non-pregnant adolescents and adults but initially parents were encouraged to use it to keep their children safe from infection, the JAMA Journal of the American Medical Association reproted. Recent events such as infant deaths have called for a recommendation change regarding the vaccine.
In 2010 California was the first state to recommend Tdap be routinely administered during pregnancy, and is now recommended by the Advisory Committee on Immunization Practices for all women between 27 and 36 weeks of gestation. In the past there has been very limited data collected on the health effects of the vaccine on the mother or baby.
To analyze the vaccine's safety the researchers looked at 123,494 women whose pregnancies ended in live birth, 26,229 of which received Tdap while pregnant. The team determined the vaccine was not linked to preterm birth or small-for-gestational age birth; it was also not correlated with hypertensive disorders during pregnancy.
The vaccine was found to slightly increase the risk of chorioamnionitis, which is an inflammation of the membranes that surround the fetus. Among women who received Tdap at any time during their pregnancy, 6.1 percent were diagnosed with chorioamnionitis compared with 5.5 percent of unexposed women. The researchers warned these results should be interpreted with caution because the magnitude of the risk is extremely small.
"Given limited prior safety data, continued widespread pertussis transmission, and current recommendations to routinely vaccinate during pregnancy, our study provides important information on the safety of Tdap vaccination during pregnancy," the authors write.
The findings were published Nov. 12 in the journal JAMA. The study was funded through a contract from the CDC. Additional funding for chart reviews came from contracts from the CDC Vaccine Safety Datalink infrastructure task order.
