A study published today in the Journal of the American Medical Association suggests that vaccinating kids against H1N1 helps protect their entire community.
The researchers set out to test the idea of herd immunity and the observation that “[c]hildren and adolescents appear to play an important role in the transmission of influenza.”
The randomized, blinded study examined 46 volunteer Canadian Hutterite colonies. Roughly 80% of children aged 3 to 15 in half the colonies were given an H1N1 vaccine. Roughly 80% of those in the other colonies were given a hepatitis A vaccine.
Comparing the two populations, the study determined that vaccinating children against H1N1 “conferred 61% indirect protection against influenza among persons who did not receive the study vaccine.” The overall conclusion:
Our data suggest that a significant herd immunity effect can be achieved when the uptake of vaccine is approximately 80% in clusters in which children and adolescents aged 3 to 15 years are immunized.
The authors also propose that elderly people may benefit more from child-based herd-immunity than from being vaccinated themselves:
Although there were relatively few elderly individuals in this population, the protective effect is likely comparable with or greater than what can be achieved by direct immunization.
Helen Branswell, medical reporter for The Canadian Press, notes that children may not necessarily be the key to herd immunity:
Dr. Allison McGeer, an influenza expert at Toronto’s Mount Sinai Hospital, questioned whether the effect was due to the fact that Loeb’s team vaccinated kids, or just to the fact that they vaccinated a sizable portion of the population of the colonies randomized to get flu shots.
The New York Times piece about the study is here. The National Institute of Allergy and Infectious Diseases press release is here.












