If you want to stop flu from spreading, start by vaccinating the kids.
That little bit of common sense just got a big scientific boost from a study that shows unvaccinated adults can be protected against flu if enough nearby children vicinity get immunized.
The idea is an old one. But the work, just published in JAMA, provides the strongest evidence so far that immunizing youngsters works to the benefit of an entire community.
Public health people call it "herd immunity." If enough individuals in the "herd" are immune, the rest have a much lower chance of infection. If the virus is the spark, there's just a lot less dry kindling lying around.
And there's no doubt that flu outbreaks are driven by children. In a typical flu season, more than 40 percent of school-age kids get the flu—up to four times the rate among adults.
In the JAMA study, Canadian researchers enlisted the help of four dozen Hutterite communities to see if vaccinating schoolkids would indirectly protect unvaccinated adults. Hutterites are Anabaptists and live in tight-knit rural religious enclaves.
In half the communities, 83 percent of children between 3 and 15 got flu vaccine — and almost no adults did. In the other half, the schoolkids got vaccinated against hepatitis A, to serve as a control group. Both study participants and medical personnel were kept in the dark about who got which vaccine.
By the end of the 2008-2009 flu season, adults living in communities where schoolchildren got flu vaccine had 60 percent lower flu rates than adults in control communities.
This isn't the first study to suggest vaccinating schoolkids protects grownups against flu. Texas researchers have compared vaccinated and unvaccinated towns; but they weren't able to separate flu cases from other kinds of respiratory illness.
Japan did an enormous "natural experiment" between 1977 and 1994, when a law required all schoolchildren to get flu shots. Wintertime flu deaths in the elderly virtually disappeared. But after the law was repealed, older Japanese started dying of flu again.
But the Japanese experience wasn't a carefully controlled study.
Now that the Centers for Disease Control and Prevention is saying everybody should get flu shots, does it matter if a study finally proves that vaccinating schoolchildren protects others? Yes, because nobody expects 100 percent of the population to get immunized, ever. So it might be smart to target schoolchildren for special efforts.