THURSDAY, Dec. 8, 2016 (HealthDay News) -- Getting a flu shot during pregnancy can protect both a mom-to-be and her baby. And while the percentage of pregnant American women who got the vaccine has doubled in recent years, too many still go without the shot, researchers say.

"Although the trend is encouraging, coverage still falls far short of the 2016 [U.S.] recommendation that all pregnant women who are or might become pregnant during flu season be vaccinated," according to a team led by Stephen Kerr, an epidemiologist at Boston University.

Kerr's team has tracked data on vaccinations received during pregnancy for more than 5,300 U.S. women since 2005. The investigators found that in the flu seasons before the 2009-2010 H1N1 flu pandemic, only one in every five pregnant women in the study got an influenza vaccine.

However, that number jumped to 33 percent of the women during the 2009-2010 flu outbreak, and has risen since then to 41 percent coverage by the 2013-2014 flu season.

Twenty percent of the vaccinations the women received were given in "non-traditional" health care settings -- such as at work or school, or in a pharmacy -- but the majority were given in doctors' offices.

The study authors also noted that the latest data from the U.S. Centers for Disease Control and Prevention showed that half of pregnant women had received a flu shot in the 2015-2016 season.

Influenza and its complications can endanger both the pregnant woman and her baby, the researchers noted. And it's thought that when a woman gets the vaccine in pregnancy, its effects may help shield a newborn from flu for several months after birth.

So, what can be done to raise flu vaccination rates further among pregnant women? According to the investigators, intervention by health care staff is key.

Kerr and colleagues noted that, according to CDC data, "during the 2015-2016 influenza season, 63 percent of pregnant women whose health care provider recommended and offered influenza vaccination received the vaccine compared with 38 percent who received a recommendation but no offer, and only 13 percent of pregnant women who received no recommendation."

This means that the routine care of pregnant women should include counseling about and administration of flu vaccine, the researchers concluded.

The findings are published in the Dec. 9 issue of the CDC's Morbidity and Mortality Weekly Report.

More information

The CDC has more on the flu shot and pregnancy.