Study Shows Vaccine in Schoolchildren Indirectly Prevents Spread of Flu to High-Risk People
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March 9, 2010 -- New research confirms that giving flu shots to large numbers of school-age children can protect the community at large.
The finding adds to evidence in favor of so-called "herd immunity" -- the idea that vaccinating the healthy and those most likely to spread the flu can have a dramatic impact on overall transmission rates.
The study was conducted in rural western Canada among the Hutterites, a branch of the Anabaptist Christian denomination. Like the Amish and Mennonites, Hutterites live in distinct communities and have limited exposure to the outside world.
During the fall of 2008, large numbers of children between the ages of 3 and 15 from some Hutterite colonies got flu shots, while children in other colonies were not vaccinated against the flu.
As a result, about half as many flu cases occurred during the first six months of 2009 in the colonies where flu shots were given.
The study appears in the March 10 issue of the Journal of the American Medical Association.
"In influenza, we have traditionally vaccinated people with the highest risk for complications, such as the elderly and those with compromised immune systems," study researcher Mark Loeb, MD, of McMaster University in Ontario tells WebMD.
"This study shows that when you immunize healthy children and adolescents who do not have a high risk for complications, you indirectly protect those at highest risk who might not be able to mount a good response to the vaccine."
Protecting the Community From Flu
In the United States, flu kills an estimated 36,000 people each year and 200,000 are hospitalized because of complications from influenza infection.
The elderly and immunocompromised are most vulnerable to flu, along with pregnant women and babies too young to be vaccinated.
Previous research has suggested that immunizing the healthy young can reduce influenza transmissions. But the study by Loeb and colleagues is the first in which some people were randomly assigned to either get a flu vaccine or remain unvaccinated.
The Hutterite colonies offered a unique opportunity for this type of study. Each colony includes approximately 60 to 120 people, but families live in individual homes. The children attend Hutterite schools from ages 3 to 15.
The study included close to 950 Canadian school-aged children and 2,326 other community members from 49 Hutterite colonies.
Children in some of the colonies were given the flu vaccine, while children in other colonies were given hepatitis A vaccine instead of flu shots.
Based on computer models, the researchers hypothesized that 70% of the children in a colony would need to be vaccinated to protect the general community. The actual average coverage in colonies where children got the flu shots was 83%.
During the 2008-2009 flu season, 4.5% of the population in the colonies where children were vaccinated against the flu got influenza, compared to 10.6% of the population in the colonies in which the hepatitis A vaccine was given.
"The risk of getting the flu was around 60% lower for people who lived in colonies where the kids got the flu shots," Loeb tells WebMD.
Vaccination of Schoolchildren
The findings mimic, on a smaller scale, the experience in Japan from the early 1960s until the late 1980s.
During this time, annual flu shots were mandatory for school-aged children and vaccination rates of between 50% and 85% were achieved.
Deaths from the flu in Japan during this period dropped threefold to fourfold, but flu-related deaths began to climb again after the mandatory vaccination law was relaxed in 1987 and later repealed.
Infectious disease specialist William Schaffner, MD, says in the U.S. about 30% of children get annual flu shots, even though the CDC has recommended routine vaccination of the young for the past four years.
Schaffner is professor and chairman of the division of infectious diseases at the Vanderbilt University School of Medicine in Nashville, Tenn.
"We have a long way to go to get to the vaccination levels that would be necessary to see this herd immunity in the general population," he tells WebMD.
Schaffner says the new findings could have important implications in years in which there are flu vaccine shortages.
Public health officials are now debating whether to recommend immunization for healthy children as well as people at high risk for flu complications in these years to reduce community-wide transmission.
Pulmonologist Len Horovitz, MD, of Lenox Hill Hospital in New York City, warns that vaccinating the healthy young is no substitute for vaccinating those most at risk from influenza.
"I would hope at-risk people don't take from this that they don't need to be vaccinated," he says. "That would be the wrong message to send."
SOURCES: Loeb, M. Journal of the American Medical Association, March 10, 2010;
vol 303: pp 943-950.
Mark Loeb, MD, MSc, McMaster University, Hamilton, Ontario, Canada.
William Schaffner, MD, professor and chairman, department of preventive medicine, division of infectious diseases, Vanderbilt University School of Medicine, Nashville, Tenn.
Len Horovitz, MD, pulmonologist, Lenox Hill Hospital, New York.
News release, Journal of the American Medical Association.
New England Journal of Medicine, March 22, 2001; vol 344.
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