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Inactivated influenza vaccine provided herd immunity
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Immunizing children against seasonal influenza in a largely self-contained religious community significantly protected unvaccinated community members against influenza as well, according to a study published online today.
Mark Loeb, MD,of McMaster University, Hamilton, Ontario, Canada, and other researchers recruited 947 children aged 36 months to 15 years from 46 Canadian Hutterite religious colonies that have limited contact with surrounding, non-Hutterite populations. Five hundred and two children in 22 colonies received 2008-2009 seasonal influenza vaccine, whereas 445 youth in the other colonies received hepatitis A vaccine. The hepatitis A vaccine served as a control vaccine for comparison.
In the six months after the children were vaccinated, 119 of 2,326 unvaccinated community members of all ages developed laboratory-confirmed cases of influenza. Of these, 80 of 1,055 were from colonies in which children received hepatitis vaccine, whereas 39 of 1,271 were from colonies in which children received the influenza vaccine.
The researchers concluded that influenza vaccination was 61% effective at indirectly protecting unvaccinated individuals if they lived in a colony where approximately 80% of the children had received influenza vaccine.
The researchers wrote that their findings “offer experimental proof to support selective influenza immunization of school-aged children … 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.”
The research was funded in part by the National Institute of Allergy and Infectious Diseases, which is part of the NIH, and the Canadian Institutes of Health Research.
Loeb M. JAMA. 303:943-950.