Studies Confirm Safety of Flu Vaccine in Pregnant Women

Kate H. Gamble, Senior Editor
Published Online: Wednesday, October 26, 2011
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Seasonal influenza vaccines can help protect newborns from the flu for months after birth and do not raise the risk of miscarriage, according to findings being presented at the annual meeting of the Infectious Diseases Society of America (IDSA) in Boston, Massachusetts this week.

Additional research being presented at the meeting suggests that an increasing number of women are realizing the importance of getting immunized during pregnancy.

“Pregnant women are understandably concerned about protecting their unborn babies, which makes it all the more important for them to understand that getting a flu shot during pregnancy is an important way to protect the baby, as well as themselves,” said Kathleen Neuzil, MD, of the University of Washington School of Medicine, in a statement. “These new data on the safety and effectiveness of these vaccines is reassuring, and the increasing number of pregnant women receiving the vaccine affirms that women are hearing the message about the vaccine’s benefits.”

Newborns are particularly vulnerable to the flu because they typically are born without protective immunity and can’t get the vaccine until they are six months old. If they get the flu, infants can become severely ill, be hospitalized and even die.

Infants whose mothers were not vaccinated are particularly vulnerable to flu because they are more likely not to be born with protective immunity and cannot be vaccinated for at least 6 months, according to IDSA data. Those that do become infected with influenza are at a higher risk of complications, and even death.

Flu vaccine protects newborns
By getting vaccinated, pregnant women are protecting themselves from getting the flu, which benefits their unborn child by keeping the disease at bay.

In a study conducted at the University of Utah, 11 (41%) of 27 women received the seasonal influenza vaccine and 16 (59%) did not. Researchers tested the antibodies in the blood of the infants at birth, 2 months, and 4 months. All infants born to immunized women had antibody protection at birth, compared to 31% of those born to women who had not received the vaccine. At 2 months, 60% of infants born to immunized women had antibody protection, and by 4 months, 11% still had protective antibodies. In infants born to unimmunized women, none of the babies had antibody protection at 2 months or 4 months.

“Our research suggests that maternal vaccination does provide some protection from the flu for a few months after birth,” said lead study author Julie H. Shakib, DO, MPH, of the University of Utah. “Pregnant women should receive the vaccine as soon as it becomes available to protect themselves as well as their babies.”

No increase in miscarriage risk
A large study looking at influenza vaccination during the first trimester of pregnancy found no association between getting the influenza vaccine while pregnant and likelihood of miscarriage.

In the study, investigators from Marshfield Clinic in Wisconson compared 243 pregnant women who had a miscarriage with 243 who did not. The analysis showed that women who miscarried were not more likely to have received influenza vaccine during the 4 weeks prior to the miscarriage compared to those who did not miscarry. Overall, 38 women (16%) who miscarried received the influenza vaccine before the pregnancy loss, compared to 31 women (13%) who did not miscarry. This difference was not statistically significant.

“Safety concerns are one of the top reasons pregnant women provide for abstaining from getting the influenza vaccine,” said Stephanie A. Irving, MS, of the Marshfield Clinic Research Foundation. “Our findings should help pregnant women feel more comfortable about getting vaccinated.”

Getting the message across
A study conducted at Christiana Care Health System in Newark, Delaware found that pregnant mothers appear to be getting the message about the benefits and safety of the flu vaccine. Results showed that 55% of pregnant women received vaccinations after 2010, compared to less than 15% before 2009.

“Although there’s still room for progress—nearly half of pregnant women still aren’t getting the vaccine—we’re encouraged that vaccination levels didn’t drop to anywhere near what they were before the H1N1 pandemic,” said Marci L. Drees, MD. “Because many pregnant women only see their obstetricians during their pregnancy, it’s important that OBs encourage pregnant women to get the vaccine and have it available, which makes a big difference.”

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