Immunizing children aged 3–15 years in isolated rural communities against influenza conferred substantial immunity to unvaccinated members of the communities, according to a report.
“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,” said Dr. Mark Loeb of McMaster University, Hamilton, Ont., and his associates.
Observational and computer modeling studies have suggested that such an approach might reduce influenza transmission, but randomized clinical trials to confirm this theory have not been feasible because in most settings, it would be unethical to withhold immunization from children in a control group.
However, rural Hutterite colonies in Western Canada offer a unique setting for such a study. These communities of approximately 60–120 Anabaptist residents are relatively isolated from other populations but show significant influenza activity each winter. The members of 46 Hutterite colonies in Alberta, Saskatchewan, and Manitoba agreed to random assignment to receive either immunization for influenza A and B during the 2008–2009 flu season (22 colonies) or to receive hepatitis A vaccination as a control (24 colonies).
Only healthy children aged 3–15 years were immunized, because those are the ages at which Hutterite children attend school. Mean vaccine coverage was 83% in this age group. This resulted in 502 children receiving flu vaccine in a population totaling 1,773 and 445 children receiving hepatitis A vaccine in a population totaling 1,500. Other colony members were not immunized, as is customary in Hutterite colonies. This includes community members at high risk of influenza complications such as children aged 23 months and younger, pregnant women, the elderly, and people of all ages with chronic medical conditions.
The primary outcome of this study was the development of laboratory-confirmed influenza A or B in colony members who did not receive flu vaccine. This occurred in 39 members of colonies assigned to influenza immunization (3%), a rate less than half of the 7.6% rate of influenza infection in control colonies.
“The level of indirect vaccine protectiveness was 61%” overall and 49% among high-risk subjects, Dr. Loeb and his colleagues said (JAMA 2010;303:943–50).
Disclosures: This study was supported by the Canadian Institutes for Health Research and the National Institute for Allergy and Infectious Diseases. Sanofi Pasteur donated vaccines used for the study but provided no funding and had no other role in the study. The authors said they had no conflicts of interest.