Influenza Vaccine During Pregnancy may Protect Both Mother and Offspring
A flu shot provided to a woman during her pregnancy can help shield her newborn against the potentially deadly infection, researchers report.
The study, conducted in Bangladesh, bolsters longstanding U.S. recommendations that pregnant women get vaccinated against influenza -- especially since it is also recommended that infants under 6 months of age not receive the shot.
"Our data show that a single dose of maternal influenza vaccine provides a considerable two-for-one benefit to both mothers and their young infants," wrote a team led by Dr. Mark C. Steinhoff, of Johns Hopkins University's Bloomberg School of Public Health, in Baltimore.
The study was published online Sept. 17 in the New England Journal of Medicine. Steinhoff was also expected to present the findings Wednesday at a Washington, D.C., meeting focused on the flu shot, sponsored by the U.S. National Vaccine Advisory Committee.
In the study, Steinhoff's group pointed out that maternal influenza infection during pregnancy carries health risks for the mother and her offspring, including fetal malformation and even infant death. In fact, "childhood deaths associated with influenza are most frequent in infants under the age of 6 months," the authors noted.
For more than a decade, experts at the U.S. Centers for Disease Control and Prevention have recommended that pregnant women get a flu shot. The vaccine is also recommended for infants between 6 and 24 months of age. It is not recommended for younger babies.
The CDC also recommends a yearly flu shot for household contacts and caregivers of children under age 5. This includes anyone who lives with children under 5, such as parents and older brothers and sisters, as well as daycare providers, babysitters, and other caregivers.
However, the researchers knew that newborns can pick up some immunity to the flu virus from maternal antibodies circulating in the fetal environment.
So, would antibodies stimulated by a flu vaccine given to the mother protect her baby?
To find out, Steinhoff's team tracked the health of a group of 340 Bangladeshi mother-infant pairs during 2004-2005. Some of the women received a flu shot during their pregnancy, while others did not. The researchers then tracked levels of respiratory illness among both moms and babies for the first 24 weeks after delivery. Infants were not vaccinated against the flu during this time.
The researchers found that babies born to vaccinated mothers had a 63 percent lower risk of laboratory-confirmed influenza compared to babies whose mothers who had not received the flu shot. The incidence of any type of respiratory illness with fever also declined, from 153 cases among infants born to unvaccinated mothers to 110 cases among babies whose mothers had gotten the flu shot.
"In other words, five pregnant women would need to be vaccinated to prevent a single case of respiratory illness with fever in a mother or infant," the team concluded. One case of laboratory-confirmed influenza among infants would be prevented for every 16 shots given to pregnant women, they found.
The researchers noted that, despite the current CDC recommendations, few expectant mothers in the United States currently receive the flu shot -- even though "the general safety of this strategy has been shown." This trial -- the first randomized, prospective study on the topic yet conducted -- offers what they call "unique evidence supporting the strategy of maternal immunization to prevent influenza infection in young infants and their mothers."
The CDC and other federal health experts will discuss the formulation and availability of the upcoming 2008-2009 seasonal flu vaccine in a press conference scheduled for Sept. 24.
Influenza Risk during pregnancy:
During pregnancy you are at risk for complications from influenza, such as pneumonia. Studies done over 17 flu seasons have demonstrated that pregnant women in their third trimester were as likely to be hospitalized for lung or heart problems as women with serious, chronic medical conditions that were not pregnant. This risk seemed to increase later in pregnancy, particularly after about week 37. Pregnant women with asthma were particularly at risk.
An analysis of decades-old serum samples from pregnant women suggests that a mother's influenza illness early in pregnancy may increase the risk of schizophrenia for her child years later. The study was funded by the National Institute of Mental Health, the National Alliance for Research on Schizophrenia and Depression, and the Lieber Center for Schizophrenia Research.
The study, published Aug 2 in the Archives of General Psychiatry, showed that the risk of schizophrenia in adult offspring increased threefold for influenza exposure during the first half of pregnancy. However, this finding fell just short of being statistically significant (P=.052). Flu in the first trimester of pregnancy was associated with a sevenfold increase in risk of schizophrenia in the offspring, but this finding also failed to achieve significance (P=.08). There was no increased risk associated with flu exposure during the second or third trimester.
While no conclusive evidence exists that vaccines are harmful for developing fetuses, the American Academy of Pediatrics (AAP) recommends that pregnant women should only receive immunizations if:
The vaccine is not deemed harmful to pregnant women and their babies
Exposure to disease risk for mother and baby is high
Resulting infection from disease would be high risk for mother or baby
Generally, live-virus vaccines are contraindicated for pregnant women because of the theoretical risk of transmission of the vaccine virus to the fetus.
In fact, vaccination with the inactivated vaccine is recommended for women who will be pregnant during the influenza season. Pregnant women are at increased risk for serious medical complications from influenza. One recent study found that the risk of influenza-related hospitalization was four times higher in healthy pregnant women in the fourteenth week of pregnancy or later than in nonpregnant women. In addition, vaccination of the mother will provide some protection for her newborn infant.
The live intranasal vaccine is not licensed for use in pregnant women. However, pregnant women do not need to avoid contact with persons recently vaccinated with this vaccine.
Vaccination is recommended for all persons, including breastfeeding mothers, who are contacts of infants or children from birth through age 59 months because infants and young children are at higher risk for influenza complications and are more likely to require medical care or hospitalization if infected. Women who are breastfeeding may receive either type of influenza vaccine unless the vaccine is not appropriate because of other medical conditions.