Sept. 17 (Bloomberg) -- Pregnant women can protect their newborns against deadly influenza infections by getting a flu shot, a study found.

Infants are particularly vulnerable to the disease because they're too young to get the annual vaccine or the drugs used to treat influenza, the researchers said. While public health officials have recommended the immunization for pregnant women for years, few mothers actually receive them, particularly in poorer countries.

The study of 340 women in Bangladesh found the shot slashed the number of proven cases of influenza by 63 percent in infants under 6 months and prevented about one in three respiratory illnesses in them and their mothers, according to the report in the New England Journal of Medicine. The protection lasted for five to six months and was similar to the benefit from the shot seen in older children.

``There's never been evidence before that immunizing the mother provides a big benefit to the baby,'' said Mark Steinhoff, a professor of pediatric and international medicine at Johns Hopkins University in Baltimore. ``That's what this study is about. More people should consider doing it,'' he said in a telephone interview yesterday.

The shots are made by Paris-based Sanofi-Aventis SA, Novartis AG, of Basel, Switzerland, GlaxoSmithKline Plc, of London, and the Australian drugmaker, CSL Ltd. The U.S. Centers for Disease Control and Prevention in Atlanta has steadily widened recommendations for annual shots to include more Americans, which now covers all children aged 6 months to 18 years.

14% of Pregnant Women

In the U.S., only about 14 percent of pregnant women are immunized. The numbers are lower in poor countries where access to health care is limited. In many of those areas, programs already exist to give pregnant women tetanus shots. They should consider adding influenza vaccines, Steinhoff said.

Every 100 flu shots prevented 14 respiratory illnesses with fevers in infants and seven infections in their mothers, the study found. The results support recommendations by the World Health Organization and others that pregnant women should get the immunization to protect themselves and their unborn children, particularly in areas where financial resources and health care is limited, the researchers said.

Influenza infections raise the risk of hospitalization in pregnant women and birth defects and other ailments for their newborns, the researchers said. Among children, death rates from the flu are highest in those under 6 months of age, according to a 2005 report in the New England Journal.

Six Cases

In the study from August 2004 to December 2005, women got either the flu shot or a vaccine against pneumococcus, a bacterium that can cause pneumonia and meningitis. There were six cases of confirmed influenza infections in children whose mothers got the flu vaccine, compared with 16 in those whose mothers got the pneumonia shot.

There weren't enough fast-acting tests for influenza available for all the women and children in the experiment who appeared ill, Steinhoff said. That may have reduced the total number of flu cases detected, because the disease can mimic other illnesses, such as common colds.

The researchers also tracked fevers, which are a common symptom of flu. There were 110 infants with fevers in the group whose mothers got flu shots and 153 in the comparison group.

The flu strikes from 5 percent to 15 percent of the world's population and kills up to 500,000 people a year, according to the Geneva-based WHO. It typically causes two weeks of fever, aches and fatigue. About 36,000 Americans die each year from it, with the greatest risk for the oldest and youngest patients, The CDC has said.

The Bill and Melinda Gates Foundation, the U.S. Agency for International Development, the Department of Health and Human Services, Wyeth, Sanofi and other organizations funded the research.

To contact the reporters on this story: Michelle Fay Cortez in Minneapolis at mcortez@bloomberg.net; John Lauerman in Boston at jlauerman@bloomberg.net.

Last Updated: September 17, 2008 09:14 EDT