Vaccinating young children and adolescents against influenza protects unvaccinated individuals in the wider community (the herd immunity), show results from a clinical trial conducted in rural communities in Canada and published free in the journal JAMA. “Our findings … support selective influenza immunisation of school aged children with inactivated influenza vaccine to interrupt influenza transmission,” writes Mark Loeb and colleagues.
Influenza is an infectious disease which causes significant morbidity and mortality; in the United States around 36,000 people die, and 200,000 people are hospitalised, each year from influenza. Vaccination against seasonal and pandemic flu is fundamental to prevent the spread of disease. Current immunisation policy targets individuals who have a greater risk of flu complications, but flu vaccines can also be used to interrupt the spread of influenza across an entire population. Previous work has shown that children and adolescents play an important role in the transmission of influenza but it is still unclear whether vaccinating these children benefits the community as a whole and protects those that have not been immunised.
Loeb et al. recruited individuals from 46 Hutterite colonies in western Canada to test the community-wide benefits of flu vaccination programmes in children and young adolescents. Their cluster trial included 947 healthy children and adolescents, ranging from 3 to 15 years old, who they randomly assigned according to community to receive either a trivalent seasonal influenza vaccine or a hepatitis A vaccine as a control. They also recruited 2,326 members from the Hutterite communities who were not vaccinated during the study. All participants in the study were followed up for signs and symptoms of influenza over a six month period.
The investigators observed that the uptake of both vaccines in eligible healthy children was similar; 83% for the influenza vaccine and 79% for the hepatitis A vaccine. 119 unvaccinated individuals had laboratory-confirmed influenza; twice as many people in the communities assigned to the control vaccine had the disease compared to those communities assigned to influenza vaccine. Loeb et al. found that this pattern of disease incidence remained even when taking into account all study participants, including those who did and did not receive a vaccine. The researchers concluded that immunising children aged 3–15 years old against seasonal flu conferred 61% indirect protection in unvaccinated people.
“Our data suggest that a significant herd immunity effect can be achieved when the uptake of vaccine is approximately 80%,” write the investigators. Their study suggests that selectively immunising children during flu epidemics may help to prevent spread of the disease in the rest of the population.
Loeb, M., Russell, M., Moss, L., Fonseca, K., Fox, J., Earn, D., Aoki, F., Horsman, G., Van Caeseele, P., Chokani, K., Vooght, M., Babiuk, L., Webby, R., & Walter, S. (2010). Effect of Influenza Vaccination of Children on Infection Rates in Hutterite Communities: A Randomized Trial JAMA: The Journal of the American Medical Association, 303 (10), 943-950 DOI: 10.1001/jama.2010.250