TUESDAY, Feb. 20, 2018 (HealthDay News) -- There's some good news for expecting moms who are trying to weather a brutal flu season -- a new study shows that getting the flu vaccine during pregnancy causes no harm to newborns.
Researchers reviewed records on more than 400,000 infants born between 2004 and 2014, and found no increased risk of infant hospitalization or death following maternal inoculation during pregnancy with either the flu vaccine or Tdap (tetanus-diphtheria-pertussis, or whooping cough) vaccine.
The study provides the longest-term look at the vaccines' effect on newborn health, with the babies followed out to 6 months of life, said study author Dr. Lakshmi Sukumaran, a pediatric infectious disease researcher with the U.S. Centers for Disease Control and Prevention.
"We didn't expect to find any increased risk in these infants," Sukumaran said. "We wanted to do this study because pregnant women are especially concerned about how any exposures during pregnancy could negatively impact their children.
"We wanted to provide reassurance that these vaccines, which are recommended for every woman during pregnancy, aren't creating a risk for the baby," she added.
A flu shot is recommended for every person older than 6 months in the United States, even though the CDC reported on Thursday that this year's vaccine is only 25 percent effective against H3N2 influenza, the cause of most illness so far this season.
That recommendation holds, the CDC says, because the vaccine is more effective against the three other major strains of flu virus, potentially preventing a second round of flu caused by another strain. Every flu shot a person receives also adds to their long-term immunity.
Additionally, among children ages 6 months to 8 years old, this year's vaccine's effectiveness is 59 percent, the agency reported.
"The flu vaccine is recommended at any point during pregnancy," Sukumaran said. "It's not too late to get the vaccine this season."
Expecting mothers are advised to get the flu shot because their immune system undergoes changes during pregnancy intended to protect the unborn fetus. "These changes also predispose women to an increased severity of influenza during pregnancy," Sukumaran said.
Pregnant women are five times more likely to die of influenza, and they also are at increased risk of flu complications and hospitalization due to their infection, she said.
The flu shot also helps their baby. The antibodies generated by the mom's immune response are shared with the fetus, providing it protection during the critical first six months of life, Sukumaran said.
The same goes for the Tdap vaccine. "Most deaths from pertussis are in very, very young babies who aren't eligible to get the vaccine," Sukumaran said. "Vaccinating the mom is a way to protect both the mom and her baby."
To assess the safety of the flu and Tdap vaccines, Sukumaran and her colleagues gathered information from the Vaccine Safety Datalink, a collaboration between the CDC and eight health care systems across the nation.
From the database, the researchers found records on more than 413,000 live births between 2004 and 2014. Of those newborns, 25,222 were hospitalized and 157 died within the first six months of life.
Comparing babies born of vaccinated and unvaccinated moms, the researchers found no association between infant deaths or hospitalizations within the first six months of life and either the influenza or Tdap vaccine.
"Hopefully, the study will help to increase immunization rates of pregnant women as they -- and the fetus they are carrying -- are at particular risk for severe complications of these vaccine-preventable infections," said Dr. Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security.
"Influenza is particularly concerning as pregnant women are disproportionally at risk for complications that range from pneumonia to miscarriage to death," Adalja said.
The new study was published online Feb. 19 in the journal Pediatrics.
The Mayo Clinic has more about vaccination during pregnancy.
SOURCES: Lakshmi Sukumaran, M.D., M.P.H., pediatric infectious disease researcher, U.S. Centers for Disease Control and Prevention; Amesh Adalja, M.D., senior scholar, Johns Hopkins Center for Health Security, Baltimore; Feb. 19, 2018, Pediatrics, online