Newborn babies whose mothers got a flu shot while pregnant are less likely to get the flu or to be admitted to the hospital with a respiratory illness in the first six months of life, U.S. researchers said on Monday.

During most flu seasons, babies under six months tend to have fewer cases of flu-like illnesses than those who are 6 to 12 months old, most likely because they are protected by their mothers' natural antibodies.

But in severe flu seasons, such as the 2009 swine flu pandemic, these youngest children, who are too young to get flu shots themselves, are more likely to be hospitalized and die from flu than older babies.

The U.S. Centers for Disease Control and Prevention has for years recommended that pregnant women be vaccinated against seasonal flu, but the study adds to other research showing that newborn babies benefit, too.

Researcher Angelia Eick, formerly of Johns Hopkins in Baltimore and now of the Armed Forces Health Surveillance Center in Silver Spring, Maryland, wanted to see if giving pregnant women flu shots could increase protection for babies under 6 months old.

Eick and colleagues studied children on Navajo and White Mountain Apache Indian reservations. In these communities, children are more prone to severe respiratory infections than those in the general population.

The team studied 1,160 mother-infant pairs over three flu seasons. The mothers and babies gave blood samples before and after the flu season and they were monitored for flu symptoms.

In the flu season following the child's birth, babies whose mother had been vaccinated were 41 percent less likely to have a lab-confirmed flu infection and 39 percent less likely to be hospitalized for a flu-like illness.

They also found babies whose mothers had been vaccinated had higher levels of flu antibodies at birth and at 2 to 3 months of age compared with babies whose mothers did not get a flu shot.

Although influenza vaccination is recommended for pregnant women to reduce their risk of influenza complications, these findings provide support for the added benefit of protecting infants from influenza virus infection up to six months, Eick and colleagues wrote in the Archives of Pediatrics & Adolescent Medicine.

The findings are particularly relevant with the 2009 H1N1 flu virus, which hit pregnant women and young babies especially hard, the team wrote.

Current flu vaccines protect against the H1N1 virus as well as two other strains of the flu.

Medicine