Noting “limited” research on the long-term safety of infants when their mother was vaccinated during pregnancy, a new study evaluates whether influenza or tetanus toxoid reduced diphtheria toxoid and whether acellular pertussis (Tdap) immunizations increase the risk of infant hospitalization or death in the first 6 months of life.

The results, published in the journal Pediatrics, are especially important because the Advisory Committee on Immunization Practices currently recommends that pregnant women receive influenza and Tdap vaccinations. The CDC advisory group recommends that pregnant women receive influenza vaccine any time during pregnancy and also advises that they receive Tdap vaccine between weeks 27 and 36.

A CDC-led study team reviewed singleton, live-birth pregnancies in the Vaccine Safety Datalink between 2004 and 2014. Looking for infant hospitalizations and mortality in the first 6 months of life, the researchers performed a case-control study matching case patients and controls 1:1 and used conditional logistic regression to estimate odds ratios for maternal exposure to influenza and/or Tdap vaccines in pregnancy.

Out of an overall group of 413,034 live births, 25,222 infants had hospitalizations and 157 infants died in the first 6 months of life. No association was determined, however, between infant hospitalization and maternal influenza (adjusted odds ratio: 1.00; 95% confidence interval [CI]: 0.96-1.04) or Tdap (adjusted odds ratio: 0.94; 95% CI: 0.88-1.01) vaccinations. In addition, receipt of the vaccinations also was not associated with infant mortality.

The study also indicates that infants hospitalized for respiratory issues had lower rates of maternal vaccination for Tdap compared to controls.

“We found no association between vaccination during pregnancy and risk of infant hospitalization or death in the first 6 months of life. These findings support the safety of current recommendations for influenza and Tdap vaccination during pregnancy,” study authors write.

Efforts to increase immunizations in pregnant women have been successful. For example, the CDC reported last fall that vaccination rates for mothers in one study had grown from less than 1% receiving Tdap vaccine before 2009 to 54% having received the vaccination.