During the 2009–2010 H1N1 flu pandemic, several groups were noted to develop more severe disease than others; pregnant women and infants were two of these groups. Numerous studies have demonstrated the heightened risk to pregnant women from both seasonal flu and the recent H1N1 and have highlighted the need to ensure vaccination of women prior to and during pregnancy.
Despite this, influenza vaccination rates among pregnant women have remained, until recently, much lower than desired. In the 2007–2008 and 2008–2009 seasons, vaccination rates were only 24.2 percent and 11.3 percent respectively. A significant increase during the 2009–2010 season, likely related to the media attention surrounding H1N1 as well as efforts to distribute the vaccine at no cost, resulted in 50.7 percent of pregnant women receiving the seasonal vaccine and 46.6 percent receiving the H1N1 vaccine. The flu vaccine is currently recommended to pregnant women during any trimester.
The recent experience is encouraging, but for a vaccine that is safe and well-tolerated, why do vaccination rates remain low? Research from the Centers for Disease Control and Prevention suggests that the recommendation of providers can have a profound effect on women’s acceptance of the vaccine. Women who received a recommendation from their health care provider to get the vaccine were 3.3 times more likely to get the vaccine than those who reported that their provider had not recommended it. Of those pregnant women who did not get vaccinated, a large percentage reported safety concerns for both the baby and themselves as reasons for refusing the vaccine. Recent research suggests they could not be more misinformed.
Beyond protecting the pregnant patient, a new study suggests that vaccinating pregnant women is associated with a protective effect on their infants. Researchers at Yale Medical School, reporting in the journal Clinical Infectious Diseases, looked at infants less than 1 year old admitted to the hospital with laboratory confirmed seasonal influenza over a span of 10 years and matched these patients with control infants admitted without influenza. Using this matched case-control design, they concluded that the vaccine, administered to their mothers while they were pregnant, was 91.5 percent effective in preventing influenza in infants younger than 6 months. There was no effect in children between 6 and 12 months. Infants younger than 6 months are at great risk, in large part because the seasonal vaccine is not recommended in this age group. Research from Finland, the only European country that has recommended and reimbursed vaccination with seasonal flu for children ages 6 months to 35 months, found that the majority of hospitalizations for infants less than 1 year were related to influenza and of those, 10 percent resulted in admissions to intensive care units. Because the seasonal flu vaccine is not recommended for use in children younger than 6 months, the Yale researchers provide a clear strategy to protect infants in this age range who are at high risk for developing complications from the flu: Vaccinate their mothers.
Erica Seiguer Shenoy, MD–PhD ’07, is a fellow in infectious disease at Massachusetts General Hospital and Brigham and Women’s Hospital.
The opinions expressed are not necessarily those of Harvard Medical School, its affiliated institutions, or Harvard University.
