Based on the findings of a new study conducted on a small number of patients, vaccine advocates are now recommending that mothers act to vaccinate their infants as early as the second trimester of pregnancy.

"Immunize the mother and you protect the infant," researcher Mark Steinhoff said.

Researcher from the Johns Hopkins University Bloomberg School of Public Health, Emory University and International Centre for Diarrheal Disease Research in Bangladesh studied 340 pregnant women in Bangladesh and compared rates of various health problems among their infants. They found that children of women who had been given the influenza vaccine during the third trimester were 63 percent less likely to suffer from a flu in the first six months of life than those who had not been vaccinated. In absolute terms, the number of flu cases fell from 16 to six. The researchers also found a 29 percent lower risk of respiratory illness among the vaccinated infants.

Influenza in early life can lead to severe and sometimes fatal complications.

The study's results were presented at a meeting of National Vaccine Advisory Committee meeting in Washington and published in the New England Journal of Medicine.

Doctors immediately hailed the study as the first proof that vaccines given to mothers can also confer protection upon their children.

"We always assumed it, but nobody's done the study before," Steinhoff said.

Not everyone is convinced. David Elliman, immunization spokesperson for the Royal College of Pediatrics and Child Health and a community health consultant, warned against a rush to vaccinate pregnant women. First of all, he said, it may be inappropriate to make generalizations based on a study conducted in Bangladesh, which probably has a much higher rate of influenza and related complications than First World nations do.

Even if the study findings turn out to apply to First World infants, Elliman said, "it may not be appropriate to immunize the whole pregnant population for the very small group of babies who are at risk."

Nevertheless, doctors in the United States and United Kingdom are already talking about vaccinating all pregnant women against influenza as early as the second trimester.

Steinhoff noted that since 1997, the U.S. Centers for Disease Control and Prevention (CDC) has recommended vaccination for all pregnant women. Only 15 percent of mothers-to-be follow this advice, however.