Pregnant women can support the health of their babies in many ways.

Eat right and exercise. Don’t smoke cigarettes or drink alcohol during pregnancy. Have regular prenatal care.

Now a new study adds, “get a flu shot,” to that list.

“We’ve known for a long time that there’s benefit to the mom, but we definitively know now that there’s benefit to the baby, too,” Dr. Julie Shakib, M.P.H., assistant professor of pediatrics at the University of Utah and lead author of the study, told Healthline in an interview. “So we all have to make sure that everyone understands that message.”

Read More: Treating a Cold or Flu When Pregnant »

Protecting Infants

In the study, published online today in the journal Pediatrics, researchers used electronic medical records to see how many infants developed flu or flu-like symptoms during their first six months of life.

The researchers compared the health of infants born to women who reported receiving the flu vaccine during pregnancy with women who had not.

Infants born to women vaccinated for the flu were 70 percent less likely to have laboratory-confirmed flu during their first six months. They were also 81 percent less likely to be hospitalized as a result.

A 2014 randomized trial published in the New England Journal of Medicine found similar benefits for newborns.

Another study, published in 2008 in the same journal, found a 63 percent drop in lab-confirmed flu for infants born to mothers who had received the flu vaccine during the third trimester.

The current study looked at a much larger number of infants than previous studies — 249,387 infants born to 245,386 women in Utah and Idaho. It also included data from nine flu seasons, from 2005 to 2014.

“The size of this study and the number of seasons adds strength to the goal of convincing more women to immunize themselves to protect both themselves and their infants during pregnancy, and the baby in the first six months of life,” said Shakib.

Read More: Why So Many Adults, Children Don’t Get Flu Shots »

High Flu Risk

Current medical guidelines recommend that all women receive a flu shot during pregnancy. This is partially to protect the women themselves.

“Influenza can be a serious infection to begin with, but in pregnancy when the immune system does not function quite as well, it can turn into a more severe situation than it would be without pregnancy,” Dr. Jonathan Schaffir, an associate professor of obstetrics and gynecology at The Ohio State University College of Medicine, told Healthline in an email.

This can increase a woman’s risk of developing pneumonia or severe respiratory problems during pregnancy, or dying from a complication caused by the flu.

These conditions can also directly impact the baby.

“In pregnant women who are having difficulty breathing due to flu or pneumonia,” said Schaffir, “the fetus may not get sufficient oxygen, which can lead to injury or miscarriage.”

As seen in the Pediatrics study, getting a flu shot during pregnancy can help the baby as well.

“In women who have been vaccinated, some of the immunity against the illness can be passed to the infant through the placenta prior to birth, or through the breast milk after — what is called ‘passive immunity,’” said Schaffir.

This is particularly important for infants under six months, whose immune systems are still developing.

A 16-year study in Finland found that children younger than six months were most likely to be hospitalized due to flu. The second-highest group that ended up in the hospital was infants 6 to 11 months old.

“Influenza is most dangerous to anyone with a weak immune system, including infants,” said Schaffir. “Influenza may even lead to death in newborns.”

Read More: When the Flu Turns Deadly »

Getting the Word Out

In the Pediatrics study, researchers found that over the course of the nine flu seasons, only 10 percent of pregnant women had been vaccinated against the flu.

This increased after the 2009-2010 H1N1 flu pandemic but still fell short of what many health professionals would like to see.

“Ideally we’d like 100 percent of women to be immunized against influenza during pregnancy for the benefit to the infant,” said Shakib.

In the study, the rates were also lower in some groups, including women with government insurance or no health insurance at all.

 “The evidence and the benefits are clear,” said Shakib. “The true work is to improve policy and improve access to flu vaccine for women, as well as provide education that promotes the importance of flu vaccine during pregnancy.”

This may also mean addressing women’s concerns about the safety of the flu vaccine.

“Often patients are reluctant to get vaccinated because they fear for the safety of the baby,” Dr. Diana Ramos, an obstetrician and gynecologist and co-chair of the National Preconception Health and Health Care Initiative, told Healthline. “They don’t know how much the components of the vaccine are going to affect or not affect their baby.”

Read More: Pursuit of a Lifetime Flu Vaccine Gains Momentum »

Addressing Women’s Concerns

One ingredient that often raises concerns is thimerosal, a mercury-based preservative that is found in certain vaccines.

This compound has been blamed for cases of autism in children, even though there is no evidence to support any link between the two.

“The small amount of thimerosal in vaccines has not been shown to have any adverse effects in pregnant women.” said Schaffir.

He added that women who still have concerns could ask for a thimerosal-free flu vaccine, which is available as a single-dose shot.

Schaffir also put the vaccine risk in context.

“Overall, the risks of influenza to a pregnant woman and her fetus are greater than any risk of the vaccine,” he said.

In addition to being vaccinated against the flu during pregnancy, mothers can take other steps to reduce their infants’ exposure to the flu.

This includes washing their hands frequently, avoiding contact with people who have the flu or other respiratory illnesses, and not touching their eyes or their infant’s eyes, nose, or mouth with unwashed hands.

Vitamin D is also frequently recommended as an alternative to the flu vaccine. A recent small study found some support for this, but more research is needed to know if vitamin D can really protect women — and their infants — from the flu.

That leaves the flu shot as the best line of defense.

“The most effective way to prevent the flu is by getting the yearly vaccine,” said Schaffir.

Ramos encourages women to talk to their health providers early on about which immunizations are right for them.

And by early, she means before women get pregnant.

This kind of “preconception appointment” is appropriate both for women who are planning a family and for other women of childbearing age.

“One in two pregnancies is unplanned,” said Ramos, “so it’s always better to be safe than sorry.”