PhotoDespite previous studies to the contrary, there are still many pregnant women who choose not to get their flu shot for fear of harming their unborn child. But new findings show that the vaccine often protects children, even when it is not as effective for moms.

Researchers from The Ohio State University conducted a study to see how flu shots affected pregnancy and found that moms-to-be who had previously gotten a flu shot had a less active antibody response in subsequent years. However, they say that the protections provided to unborn children were not affected, and that getting an annual flu shot is still recommended.

"The good news is that we found that the benefits of maternal vaccination for the baby were not affected by prior vaccination in the mothers," said researcher Lisa Christian. "Women who get a flu shot year after year will likely see their initial antibody response weakened over time, but these data suggest it does not meaningfully affect protection in their babies. This is of clinical importance because many people are vaccinated annually, as recommended."

Providing protection for babies

The researchers came to these conclusions after administering a flu vaccine to 141 pregnant women, 91 of which had received a flu shot in the previous year and 50 who hadn’t. After analyzing outcomes, they found that women who hadn’t had a flu shot in the previous year had stronger initial immune responses to the vaccine.

"The flu shots help us develop antibodies to protect us from the flu virus. However, not everyone shows the same antibody responses to the vaccine,” explains Christian. “One key factor that can affect antibody responses is repeated vaccination. Growing evidence shows that those who received a flu shot in the prior year have lower antibody responses in the current year.”

While the results reinforced previous findings for adults, the researchers were curious to see how effective the vaccinations were for unborn children. To find out, they tested the pregnant women throughout their pregnancies and, upon delivery, tested blood from the umbilical cord to see if the vaccine had adequately transferred to the baby while it was in the womb. They found that the flu shot provided protections to the baby regardless of the mother’s immune response.

“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,” Christian said.

The full study has been published in Vaccine.

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