Annual flu jabs can make vaccine less effective in pregnancy

Pregnant women are among those most at risk for complications from flu, but experts have never been exactly sure how influenza vaccinations affect pregnancy.

While doctors have long recommended flu vaccinations for mums-to-be, experts have not been able to identify how exactly the shots affect pregnancy. Brand new research, published today, has revealed that pregnant women who get flu vaccinations regularly have a weaker peak antibody response to the vaccine than women who don't get them regularly, though mothers and their babies in both groups were well-protected at the time of delivery. Researchers from the Ohio State University Wexner Medical Centre administered the flu vaccine to 141 pregnant women, 91 of whom received a flu shot in the previous year, and 50 who had not. The results, published in the journal Vaccine, found that women who hadn't received a flu shot in the previous year had better initial immune responses to the vaccine. For those who had received a flu shot the previous year, their peak antibody responses were weakened. Professor Lisa Christian says in order to see how the vaccine response may affect babies, the research team tested women throughout their pregnancy and, after delivery, tested blood from the umbilical cord to see how well protection against the flu had been transferred to the baby while in the womb:

"The flu vaccines help us develop antibodies to protect us from the flu virus. However, not everyone shows the same antibody responses to the vaccine. 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. We launched this study to not only track how prior vaccination affects immune responses in expectant mothers, but also to see whether it affects how well antibodies against the flu are transferred from the mother to the baby."

Professor Lisa Christian analyses data about flu vaccines in pregnant women with a colleague at The Ohio State University Wexner Medical Centre. (Photo Credit: Ohio State University Wexner Medical Centre)

Dr Christian, who is a clinical health psychologist, says that annual vaccination is still the best way for pregnant women to protect themselves from the flu:

"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. Women who get a flu vaccine year after year will likely see their initial antibody response weakened over time, but these findings suggest it does not meaningfully affect protection in their babies. This is of clinical importance because many people are vaccinated annually, as recommended."

The Ohio team note that, although prior vaccination may modestly lower clinical protection from vaccination in the current year, annual vaccination is still the best way for people to protect themselves from the flu:

"All women should get the flu vaccination during pregnancy because it's a time of high risk for complications from the flu and, until they are six months of age, babies can't get their own flu shots, so the only way to protect them in the first few months of life is for the mother to get a flu shot during pregnancy."

The HSE advise that the vaccines have been safely administered to millions of pregnant women in the last ten years and say that the next vaccine campaign will launch in September:

"Reactions are generally mild and serious side effects are very rare. If you are already pregnant the vaccine should be given in September/October each year and is available from your family doctor or pharmacist. In the Northern Hemisphere the flu season lasts from October to the end of April. Women who become pregnant at any stage during the flu season should get the flu vaccine."