HealthMatters
We’ve known for some time that getting vaccinated during pregnancy can protect infants during those first few months of life when they’re most vulnerable. This is key because some vaccines are not available for infants less than six months of age, including the flu vaccine. But what we haven’t known is how effective it is for infants to receive the vaccine in utero, and when it is most effective to give during pregnancy.
Answering those unknowns was the motivation for a recent study published in JAMA Pediatrics, for which my colleague, Mary Staat, MD, MPH, and I were co-authors. Because Cincinnati Children’s is a part of the CDC’s New Vaccine Surveillance Network (NVSN), we can look at the data from consenting patients entering clinics, emergency rooms, and hospitals with respiratory and gastrointestinal illnesses. So for this study, we looked at national data from more than 3,700 infants to see how many entered ERs for flu-related complications; and for those who did, we worked backwards to see if and when their mothers had been vaccinated against the flu during pregnancy.
We found that for the mothers who got vaccinated during pregnancy, the flu vaccine was most effective when given in the third trimester and helped those infants younger than three months of age the most. In fact, it reduced the risk of flu in infants younger than six months by one-third, and flu-related hospitalizations by 40 percent.
Any given winter, flu-related complications are common. As many as nine percent of all infants less than six months of age may require a visit to a clinic, ER or hospital ward. And with only half of the pregnant people receiving the flu vaccine both in this study and nationally, we’re missing a large opportunity to improve the health outcomes for both moms and newborns. That’s why I’d like to share some additional information to help them make informed decisions about receiving the flu vaccine in the third trimester:
Top 3 Reasons to Get the Flu Shot in Third Trimester
1. Babies Get More Antibodies
When we vaccinate in the third trimester of pregnancy, babies receive more antibodies via the placenta. It takes about 2-4 weeks for our bodies to make antibodies, so babies in utero will receive the most right before they’re born, thus protecting them more. Again, this is important because they’re most vulnerable to flu complications and hospitalizations during those first few months of life.
2. We Can’t Predict Which Babies Will Have Severe Flu Complications
Influenza is a challenging virus because it changes from year to year. Further, some babies get flu and are fine, and others will need the intensive care unit (ICU). We currently have no reliable way of predicting which ones will simply get a fever and which ones will need oxygen and other support in the hospital.
3. It’s a Win-Win
It’s a win-win because the flu shot protects both babies and pregnant people. They are more likely than non-pregnant people to have flu complications, such as hospitalizations, premature births, and pregnancy loss. We think this might be due to their decreased lung capacity and immune systems not functioning quite the same as when they are not pregnant.
The best timing during pregnancy to get the flu shot is a bit tricky, especially if they’re in their first or second trimesters during peak flu season. We don’t want to delay the shot during this period; yet we also want their baby to get the best possible protection. So we plan to study how to balance this, which could include the possibility of multiple doses. For now, pregnant people should discuss flu shot timing with their doctors.
At first glance, this study might seem like old news. However, this is the first time we’ve been able to say what time frame is best to vaccinate during pregnancy in order to protect babies and just how effective it is for babies. The CDC estimates that the flu caused anywhere between 100,000-710,000 hospitalizations each year between 2010-2022, and vaccination is the easiest and best way to protect our babies during those first few months of life. Receiving a flu vaccination during pregnancy is just as important as RSV, Tdap, and COVID vaccines (depending on the time of year).
To learn more about Infectious Diseases at Cincinnati Children’s, or to schedule an appointment, please call 513-636-4578.
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