The short answer is that we do not know yet. But researchers have found a potential link between the flu vaccine and early-pregnancy miscarriage. According to the results of a recent study, women who received a particular version of the flu vaccine two years in a row had higher rates of miscarriage than women who did not receive the vaccine. This is the first study that has focused on the effects of repeated flu vaccines during pregnancy, and it’s the first to identify this link.
The study was published in the journal Vaccine. Researchers at the Marshfield Clinic Research Institute in Wisconsin compared 485 pregnant women who had a miscarriage to 485 pregnant women who had healthy deliveries. Only four women who had normal deliveries had received the flu shot in the preceding 28 days and had been vaccinated the year before. However, 17 women who had miscarried had received the flu shot in the preceding 28 days and had been vaccinated the previous year. There was no link with miscarriage more than 28 days after the women were vaccinated. Researchers stressed that they only saw the link in women who had been vaccinated the previous year and during their pregnancy.
One possible explanation is the makeup of the flu vaccine. After the H1N1 pandemic in 2009, vaccine manufacturers started developing vaccines that protect against the new flu strain. In the 2010-2011 flu season and the 2011-2012 flu season, the vaccine compositions were identical. More pregnant women also received the flu shot during and after the H1N1 pandemic, so they may have had an immunological response after receiving the same vaccine two years in a row.
Experts say that the study’s results indicate an association between repeated vaccines and miscarriages, but this doesn’t necessarily mean that the vaccines cause miscarriages. Amanda Cohn, a senior adviser at the CDC, says, “We need to understand if it’s the flu vaccine, or is this a group of women who were also more likely to have miscarriages.”
Those involved with the study also say that because the research is so new and is not yet well-understood, women should still follow advice from medical professionals to get a flu vaccine. Influenza during pregnancy can cause miscarriage and serious birth defects. Infants can’t receive the flu vaccine until they’re six months old, so vaccination during pregnancy is also helpful for protecting newborns. However, this study raises some new questions about flu vaccine safety during pregnancy.
CDC Insists Flu Vaccine is Safe for Pregnant Women, Future Studies Planned
Health officials understand that pregnant women might be concerned about this study, so the CDC posted a guidance explaining the study and encouraging pregnant women to discuss the best timing for their flu vaccine. The CDC also listed several previous studies that show that flu shots are completely safe during pregnancy.
The CDC is working on a long-term study involving pregnant women who have received the flu shot more than three times since 2012. The results should be completed in late 2018 or 2019, and the study should provide more detailed information about the effects of the vaccine on pregnancy.