Giving the flu shot to children protects community

Vaccinating children and adolescents against influenza can provide the same level of protection for the wider community.

This groundbreaking finding is the result of a study led by McMaster University infectious disease expert and physician Mark Loeb. The professor in the Michael G. DeGroote School of Medicine led a team of investigators from Canada and the United States to study whether selective immunization of healthy youngsters could prevent the spread of the flu in the wider community.

To conduct the study, Loeb and his team recruited participants from Hutterite colonies in western Canada who, although relatively isolated from cities and towns, still experience influenza infections and outbreaks.

The study included 947 healthy children and adolescents aged three to 15 in 49 colonies in Alberta, Saskatchewan and Manitoba. The children were randomly assigned a standard dosing of seasonal flu vaccine or hepatitis A vaccine, which was used as the control.

The study also recruited 2,326 community members who did not receive the vaccine, in order to assess the indirect effect of immunizing children and adolescents.

The researchers found that giving the flu shot to children and adolescents reduced the incidence of influenza by about 60 per cent in individuals who did not receive the vaccine. They also found that when they looked at the whole community, including the children who were immunized, the overall benefit was about the same.

"These results demonstrate conclusively that immunizing children provides a large indirect benefit to people who do not receive the vaccine, to the extent that the protection provided is comparable to directly vaccinating people who are older or at high-risk for the flu," Loeb said.

The researchers concluded that giving healthy children and adolescents the influenza vaccine significantly protected unimmunized residents of the communities against the flu. They suggest that this 'herd immunity effect' can be achieved when approximately 80 per cent of healthy children and adolescents are immunized.

"Our study provides rigorous evidence showing that immunizing children and adolescents can stop the spread of influenza. In our opinion, this has important public health implications."

Current vaccine policy focuses on immunizing people at high-risk of complications of the flu, such as those with chronic medical conditions, people 65 years and older, children under age two and pregnant women.

According to the Public Health Agency of Canada, influenza affects up to a quarter of Canadians each year. While most recover, the virus also results in about 20,000 hospitalizations and 2,000 to 8,000 deaths annually.

"Dr. Loeb's research will help us better understand how immunization can inhibit the spread of influenza and other infectious diseases," said Dr. Marc Ouellette, scientific director of the Institute of Infection and Immunity at the Canadian Institutes of Health Research. "The more we understand about the best methods and procedures for immunizing populations, the greater the chance we have at preventing the spread of infectious disease in the future, reducing illness and fatalities amongst vulnerable segments of the population."

The results of the study have been published in the March 10 issue of the Journal of the American Medical Association (JAMA). Funding for the randomized control trial was provided by the Canadian Institutes of Health Research and the U.S. National Institute for Allergy and Infectious Diseases.

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