Pregnant women who come down with the flu are at greater risk of illness requiring hospitalization. A new study found that in resource-poor countries, flu vaccination reduced the risk of illness to mother and baby.  

An estimated 40 percent of the world’s population lives in subtropical and tropical zones, where influenza sometimes circulates year-round. Yet influenza vaccine is rarely used.

Mark Steinhoff is director of the Global Health Center at Cincinnati Children’s Hospital in Ohio. He said the influenza virus, which is often mild in healthy people, can result in hospitalization of pregnant women.  

With a growing fetus pressed up against their lungs, Steinhoff says, women with the flu can have trouble breathing.  He also said a pregnant woman is  more susceptible to illness as the growing baby siphons off her natural defenses.

But in a first-of-its-kind study, Steinhoff and colleagues found vaccinating women year-round in a developing country, Nepal near the Indian border, dramatically reduced the incidence of influenza in mothers and benefited their babies.

The study was published in the journal Lancet Infectious Diseases.

“It reduced disease in the mothers and in the infants by about 60 percent reduction in the second year. It’s really quite remarkable. But it also reduced the rate of low birth weight — that is, kids born less than 2.5 kilos. It reduced that by 16 percent,” said Steinhoff.

Babies benefited from the shots because they received antibodies against the illness from their mothers while in the womb.

The study

The study ran between April 2011 and September 2013 and involved a total of 3,693 mothers between the ages of 15 and 40.   

There were two phases of the trial, with one group of women being vaccinated in the first year and a different group of pregnant women the following year.  Half of the women received a placebo.

Because influenza in some countries can circulate year-round, there’s no particular flu season as in more temperate climates. The women were therefore vaccinated at various times with a shot that contained three inactivated flu strains. Each group was followed for up to 180 days to see whether they developed fevers and body aches.

Steinhoff said the benefits of influenza vaccination have long been known in the United States and other Western countries.

“The vaccine you know was developed many years ago. It was known to be safe. There were no bad reactions to it,” Steinhoff said.

He said it’s up to individual countries to decide whether they want to launch influenza vaccination campaigns for pregnant women. In the meantime, he said, researchers will be obtaining additional data on year-round immunization programs in developing countries.

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