Immunizing children aged 3-15 years in isolated rural communities against influenza conferred substantial immunity to unvaccinated members of the communities, said Dr. Mark Loeb of McMaster University, Hamilton, Ont., and his associates.
“Our findings offer experimental proof to support selective influenza immunization of school-aged children with inactivated influenza vaccine to interrupt influenza transmission,” they wrote (JAMA 2010;303:943-50).
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. 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.
The primary outcomeof s 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.
There were six outbreaks of influenza in the vaccinated colonies, with 3-16 cases in each outbreak. In contrast, there were more than twice as many outbreaks (13) in the control colonies, with 4-26 cases in each outbreak.
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. The authors said that they had no conflicts of interest.