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Maternal flu shot offers far-reaching protection




WASHINGTON – The influenza vaccine is highly recommended for pregnant women, protecting the woman, the newborn, and even the fetus, according to Dr. Sonja Rasmussen.

Multiple prospective and retrospective studies have shown that the inactivated influenza shot is safe and effective for pregnant women. And not only does it confer a transient passive immunity upon the newborn, the vaccine also guards against the dangers the flu poses to fetuses, she said at the annual meeting of the American College of Obstetricians and Gynecologists.

Among the benefits seen with the flu shot are healthier birth weights, less preterm birth, and a much lower risk of birth defects that are associated with maternal fever in the first trimester, said Dr. Rasmussen, director of public health information dissemination at the Centers for Disease Control and Prevention.


“Fever in the first trimester doubles the risk of neural tube defects in the fetus,” said Dr. Rasmussen. She cited a 2014 meta-analysis that found increased risks of other fetal anomalies associated with first trimester flu: hydrocephaly (odds ratio, 5.74), congenital heart defects (OR, 1.56), cleft lip (OR, 3.12), limb abnormalities (OR, 2.03) and digestive system defects (OR, 1.72) (Hum Reprod. 2014 Apr;29[4]:809-23).

“We don’t know if these are more due to the hyperthermia of fever or to the flu virus crossing the placenta,” she said. “But we do know these are real risks.”

Newborns come with an immature immune system that takes a while to get ramped up. In the first 6 months of life, they’re especially vulnerable to communicable illnesses, and they can become severely ill and even die from flu, Dr. Rasmussen said. A new study of nearly 250,000 mother-child pairs confirmed that maternal vaccination reduces the risks of flu hospitalization by more than 80% in infants younger than 6 months (Pediatrics. 2016 May 2. doi: 10.1542/peds.2015-2360).

For most women, the understanding that a flu shot protects their baby before and after birth is good enough reason to get one, Dr. Rasmussen said, but the benefits for the woman are extremely important. “Pregnant women experience a lot of changes in immune function and heart and lung function that increase the risk for complications from influenza. In prior pandemics, we have seen pregnant women at an increased risk of severe illness, hospitalization, and death.”

She cited data from the 2009 H1N1 epidemic that showed that 5% of those who died from H1N1 flu were pregnant women, despite the fact that they represented only 1% of the U.S. population (JAMA. 2010;303[15]:1517-25).

Despite the well-documented benefits and reassuring safety data, flu vaccine coverage remains suboptimal for pregnant women, Dr. Rasmussen said. The most recent CDC data suggest that just half of pregnant women were immunized in 2014-2015, a rate that has remained steady since 2012.

The most effective way to boost this number, Dr. Rasmussen suggested, is to stress to women that the vaccine protects both the fetus and newborn from a potentially fatal illness. “We know that a large number of babies and children die of influenza every year,” she said. “The biggest motivator for moms is their desire to protect their baby – much more so than protecting themselves.”

Dr. Rasmussen reported having no relevant financial disclosures.

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