Despite Weakened Antibody Response, Annual Flu Shot Protects Pregnant Women & Infants

The Centers for Disease Control and Prevention (CDC) recommends that pregnant women receive the flu shot, and now, in a new study, researchers have examined the antibody response to the vaccine in pregnant women and their babies.

Since 2010, the CDC estimates that there have been 140,000 to 700,000 flu-related hospitalizations and as many as 56,000 associated deaths in the United States. The influenza vaccine works to protect individuals from falling ill with the flu by triggering the body to make the antibodies needed to fight off the virus. Health experts recommend that pregnant women receive the flu vaccine, as they are at higher risk of developing severe flu illness if they are infected because of changes in the immune system that occur during pregnancy. Pregnant women who get the flu may also be at greater risk for complications, such as premature labor.

In a study in 2016, however, researchers found that pregnant and lactating women may be turning down the flu shot because of mixed messaging from flu vaccine manufacturers on the benefits of and precautions for receiving the shot during pregnancy. Conversely, another study found that pregnant women are increasingly opting to get the flu shot; however, those vaccination rates still fall below targets set by the CDC.

A new study published in the journal Vaccine, and led by researchers from The Ohio State University Wexner Medical Center, looked at the antibody response to flu vaccination in pregnant women and their newborns to determine how the vaccine impacts pregnant women.

“We know in normal situations flu shots help us develop antibodies to protect us from the flu virus, but when it comes to understanding exactly how vaccines impact pregnancy, our understanding has been somewhat lacking,” said study author Lisa Christian, PhD, in a recent news release.

The researchers noted that receiving a prior flu vaccine can reduce the body’s antibody response in subsequent vaccinations, and so they wanted to study the potential implications in pregnant women and their babies.

The study team measured the concentration of influenza antibodies in 141 pregnant women prior to vaccination, 30 days after vaccination, and in maternal and cord blood collected at delivery. Of the 141 women, 91 had previously received the flu vaccine, whereas 50 had not received it the previous year. The women who had previously received the flu vaccine exhibited higher baseline flu antibody concentrations against all 4 virus strains included in the vaccine and decreased antibody response 1 month after vaccination for all flu strains. However, the researchers found that prior vaccination did not affect either the antibody levels at delivery or those transferred by the women to their babies.

“The good news is; this study showed that the benefits of a flu shot to the baby were not affected in either group,” Dr. Christian said in the release. “Women who get a flu shot year after year will likely see their initial antibody response weaken over time, but it’s ultimately not going to affect their babies. Our study found that by the time of delivery, both mom and baby were well-protected.”

The CDC says pregnant women can safely receive the flu vaccine during any trimester, and that breastfeeding mothers should receive the flu shot to protect themselves from getting the flu and passing it on to their babies.