Immunizing children and adolescents with inactivated influenza vaccine resulted in reduced rates of influenza in their community compared to a similar community in which children did not receive the vaccine, suggesting that vaccinating children may help prevent transmission of the virus and offer protection for unimmunized community residents, according to a study in the March 10 issue of JAMA.
Influenza is a major cause of illness and death, resulting in an estimated 200,000 hospitalizations and 36,000 deaths annually in the United States alone. "Current vaccine policy focuses on immunizing those at high risk of complications of influenza. As a component of a broader policy to prevent the spread of influenza and reduce its complications, using immunization to interrupt community-wide transmission of influenza may be effective for protecting the entire population, including those at high risk," the authors write. They add that children and adolescents appear to play an important role in the transmission of influenza, and that selective vaccination against influenza among this group may interrupt virus transmission and protect those not vaccinated.
Mark Loeb, M.D., M.Sc., of McMaster University, Hamilton, Ontario, Canada, and colleagues assessed whether vaccinating children and adolescents with inactivated influenza vaccine could prevent influenza in other community members. Because randomizing entire communities to test the indirect benefit of vaccinating children and adolescents against influenza is not feasible in most settings, the researchers conducted their study among Hutterite (of the Anabaptist faith) colonies, which are rural communities found mostly in western Canada. "These tightly knit communities resemble extended families but are composed of single families each residing in their own house, where children and adolescents between the ages of 3 years and 15 years attend school. Approximately 60 to 120 people reside on each colony," the authors write.
This trial included 947 Canadian children and adolescents ages 3 to 15 years who received study vaccine and 2,326 community members who did not receive the study vaccine in 49 Hutterite colonies in Alberta, Saskatchewan, and Manitoba. Follow-up began in December 2008 and ended in June 2009. Children were randomly assigned according to community to receive standard dosing of either inactivated trivalent influenza vaccine or hepatitis A vaccine, which was used as a control.
The average vaccine coverage among healthy children of clusters assigned to the influenza vaccine was 83 percent, which was similar to the average vaccine coverage among colonies assigned to hepatitis A vaccine (79 percent). Laboratory-confirmed influenza was detected in 119 nonrecipients: 39 (3.1 percent) in the colonies assigned to influenza immunization and 80 (7.6 percent) in colonies assigned to hepatitis A. The level of indirect vaccine protective effectiveness was 61 percent.
Among all study participants (those who were and those who were not vaccinated), 80 of 1,773 (4.5 percent) in the influenza vaccine colonies and 159 of 1,500 (10.6 percent) in the hepatitis A vaccine colonies had confirmed influenza illness for an overall protective effectiveness of 59 percent. No serious vaccine adverse events were observed.
"Considering for instance the rapid spread of influenza A(H1N1) in the 2009 pandemic, understanding whether influenza transmission can be prevented or reduced by immunizing children is of high priority so that groups such as pregnant women and aboriginal populations who are at high risk of complications may potentially be indirectly protected," the authors write.
"Our findings offer experimental proof to support selective influenza immunization of school aged children with inactivated influenza vaccine to interrupt influenza transmission. Particularly, if there are constraints in quantity and delivery of vaccine, it may be advantageous to selectively immunize children in order to reduce community transmission of influenza."