Canadian vaccination study proves 'herd immunity'

CHICAGO (Reuters) - Inoculating children against flu protects more people of all ages in the larger community, probably because young people tend to spread viruses through physical play, Canadian researchers said on Tuesday.

Researchers at McMaster University in Hamilton, Ontario found there were 61 percent fewer flu cases in isolated communities where children and adolescents received the seasonal influenza vaccine, compared to communities where children received an unrelated vaccine.

Targeting children with a vaccine could protect the wider population, researcher Mark Loeb and colleagues concluded in their report in the Journal of the American Medical Association.

Influenza struck 2,326 unvaccinated participants in the 46 religious Hutterite communities in western Canada that were chosen for study because they have limited outside contacts.

In communities where roughly four out of five children aged 3 to 15 were vaccinated, 3.1 percent of the people got the flu compared to a 7.6 percent infection rate in communities where no one was vaccinated against flu.

This demonstrated the widely-accepted concept of "herd immunity" -- that vaccination programs can still be effective even if not everyone is vaccinated -- which could have public health implications, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

"Before, the healthy adolescent kids were not among those that were highly recommended to get vaccinated," said Fauci, whose NIAID is part of the U.S. National Institutes of Health, which helped fund the study.

"Now, this shows that even though they don't usually get into trouble from the flu, you can get double bang for the buck by protecting not only them but the people they come in contact with."

For instance, if there was a shortage of flu vaccine, it might be more effective to vaccinate the young, even though the flu presents less of a danger to them, because their rough-and-tumble socializing habits can easily spread viruses.

Last month, vaccine advisers to the U.S. Centers of Disease Control and Prevention recommended everyone over the age of six months should receive seasonal flu vaccines every year.

Seasonal flu is blamed for 36,000 U.S. deaths each year.

Fauci said the same universal vaccination policy might apply against the pandemic H1N1 virus known as swine flu, which the CDC estimated has killed about 12,000 Americans.

"Now that we're talking about vaccinating everyone, this (idea of selective vaccination of children) becomes a little bit of a moot point," Fauci added in a telephone interview.

(Editing by Maggie Fox)