Vaccinating children first reduces incidence of flu: Study

It comes too late for H1N1, but not for the next flu outbreak: New Canadian research shows vaccinating healthy children and teens first halts the spread of influenza.

The study, which involved dozens of Hutterite colonies in Western Canada, found that immunizing children age three to 15 with flu shots formulated for the 2008-09 flu season reduced the incidence of flu by about 60 per cent among people who were not vaccinated.

The data suggests such substantial "herd immunity" in an entire community can be achieved if about 80 per cent of schoolchildren are immunized during a flu outbreak.

The study appears in this week's issue of the Journal of the American Medical Association.

Children are one of the main vectors of transmission, because they gather in groups.

"There's a lot of evidence that children are the ones that initially will spread influenza in the community," said McMaster University infectious disease expert Dr. Mark Loeb, who led the study.

But healthy kids traditionally have been near the bottom of vaccine priority lists, with first preference going instead to those at high-risk of flu-related complications, such as the elderly and those with underlying health conditions. During the fall wave of pandemic H1N1, healthy children over five were among the last to be immunized.

"This study would suggest these types of policies need to be rethought," Loeb said.

The research involved residents of 49 Hutterite colonies from Alberta, Saskatchewan and Manitoba, tight-knit religious communities where about 60 to 120 people reside in each colony. A total of 947 children participated in the trial. In half the colonies, children received the seasonal flu shot; in the other half, children received hepatitis A vaccine. Loeb says hepatitis A shots were an ideal "control," because hepatitis A is known to cause outbreaks in Hutterite communities.

Loeb said the hepatitis A vaccine was chosen as a "control" vaccine because "it could benefit the participants at the same time" and it has previously been used as a control in other influenza studies.

Families knew that their children would get either the flu vaccine, or the hepatitis A vaccine. They just didn't know which one they would get.

Of those children vaccinated, 502 were in the influenza group, and 445 were in the hepatitis A group. The researchers and research nurses were completely "blinded," as were the Hutterites, as to which colony got which vaccine. The study also recruited 2,326 community members who weren't immunized in order to measure the indirect effect of just vaccinating children.

Participants were followed from December 2008 to June 2009. Nurses went to each colony twice a week, doing swabs to detect flu if someone had symptoms. Blood samples were also drawn to check for antibodies that would suggest a flu infection.

The researchers found that the flu vaccine was 61 per cent effective in indirectly preventing illness in unvaccinated people if they lived in a colony where about 80 per cent of children received the flu shot.

"Overall, if you actually include the children as well, the overall benefit was 60 per cent," Loeb said.

"That's a substantial amount of protection. If you look at the people who would be at high risk, the level of protection in them was almost the same as if they had gotten a vaccine directly themselves."

There were about half as many outbreaks of flu in the colonies that received the flu shots.

Loeb said high-risk groups should continue to be given vaccine priority.

"But, above and beyond this, immunizing healthy children and adolescents can actually stop the spread to begin with in the community, and protect more people."

Whether it's garden-variety seasonal flu or pandemic flu, "the implications are the same," he said. "By targeting children and adolescents selectively, trying to get high uptakes of influenza vaccines in these age groups, one can prevent the spread of the flu."

That's especially important when vaccine supplies are strained, Loeb said.

One strategy could be to vaccinate kids at school, he said.

The research was funded in part by the National Institute of Allergy and Infectious Diseases (NIAID), part of the U.S. National Institutes of Health, and by the Canadian Institutes of Health Research.

"It's quite an important study," said NIAID director Dr. Anthony Fauci.

"The general philosophy has been over the years that you don't really need to vaccinate young adolescents and children in school, because they're very healthy and when they do get sick (with flu) they don't usually get seriously ill," Fauci said.

But kids are exquisitely efficient at spreading flu within their homes, schools and communities, he said.

The study "proves the concept of herd immunity, where if you put immunity to a certain segment of the population, then everyone gets protected," Fauci said.

The Public Health Agency of Canada said it followed the scientific evidence that was available at the time in designating priority groups for the H1N1 vaccine.

"Our approach was to ensure that those who needed the vaccine most got it first," the department said in a written statement.

"In the event of another pandemic, we would make our recommendations for who should receive the vaccine based on similar factors. We would use the available evidence of who was most at-risk of serious complications from the virus to make recommendations on how to roll out immunization programs."