PHILADELPHIA — Pregnant women who get the flu vaccine are less likely to have babies who are premature or are small for their gestational age, according to two new studies.
Another study shows that the vaccine is safe throughout pregnancy — even during the third trimester.
Experts meeting at the annual meeting of the Infectious Diseases Society of America say they hope the findings will persuade more pregnant women to get a flu shot.
"The studies emphasize the importance of vaccination during pregnancy not only for the benefit of the mom, but for the baby," said Vanderbilt University's William Schaffner, head of the IDSA's immunization work group.
Schaffner, who moderated a news conference to discuss the findings, told WebMD that vaccination rates during pregnancy are "dismal. One estimate says that only 25 percent of pregnant women [get a flu shot]. That means that three in four don't."
While the studies did not involve women vaccinated with the H1N1 swine flu vaccine, Bruce Gellin, director of the Health and Human Services Department National Vaccine Program Office, noted that the swine flu vaccine is made the same way as the seasonal flu vaccine and there are no differences in terms of safety.
One study, led by Saad Omer of Emory University in Atlanta, showed that vaccination in pregnancy lowers the chance of having a low birth weight or premature baby.
Omer and colleagues looked at the medical records of more than 6,400 babies in Georgia from June 2004 through September 2006. About 15 percent of their moms got a flu shot during pregnancy. Results showed that during periods of widespread flu activity, vaccinated women were 60 percent to 70 percent less likely to have an infant small for his or her gestational age or have a premature baby.
In another study, vaccinated mothers in Bangladesh gave birth to babies who were 1.5 pounds heavier, on average, than those born to unvaccinated women.
Previous findings from the study showed that infants born to vaccinated women were 63 percent less likely to get the flu and 29 percent less likely to have a respiratory ailment accompanied by fever. The vaccinated moms were also less likely to get sick themselves, says researcher Mark Steinhoff of Cincinnati Children’s Hospital Medical Center.
"When you prevent flu in a pregnant woman, you benefit the mother, you benefit the infant, and we think this also shows that you benefit the fetus,” Steinhoff told WebMD.
The experts say there a variety of reasons pregnant women don't get vaccinated. In many cases, their ob-gyns don't offer it, Schaffner says. Also, mothers have a long tradition of not taking anything they fear will harm their fetus and without reassurance, they may fear the vaccine is harmful, he says.
Not only does the new research suggest the opposite, Schaffner says, but one study also shows that inactivated flu vaccine can be safely given during any trimester of pregnancy.
Researchers reviewed 11 studies of flu vaccination during pregnancy, as well as CDC data about disease and death from flu infection. Seven of the studies involved women in their third trimester.
The pooled analysis, which is published online in the American Journal of Obstetrics & Gynecology, notes that no study has shown an increased risk of maternal or fetal complications associated with the inactivated flu vaccine shot.
Also, CDC data show that in spring 2009, 32 percent of 34 pregnant women with confirmed or probable cases of H1N1 had to be hospitalized, and pregnant women accounted for 13 percent of all deaths from H1N1 during that time, says Omer, who worked on the study.
One study shows that healthy pregnant women are 18 times more likely to be hospitalized from flu than their counterparts who aren't pregnant. And pregnant women with other medical problems are at even greater risk.