Public Health

One Dose Of H1N1 Vaccine Or Two?

Even kids can get by with a single dose of swine flu vaccine, says the World Health Organization. But the U.S. is not so sure just yet.

WHO previously recommended two shots for kids younger than 10. But the new one-shot deal contradicts current U.S. policy, which calls for two shots (or nasal spritzes) in this age group.

After a two-day meeting in Geneva, WHO officials acknowledge data are sparse on whether a single dose protects younger kids against the new H1N1 virus. But vaccine shortages have forced them to reconsider.

"The priority is to give...one dose rather than vaccinate half the number of children with two doses," says Dr. Marie-Paule Kieny, director of WHO's Initiative for Vaccine Research.

US officials seemed surprised at the WHO statement.

More data on young children's response to a single dose of vaccine are expected in the next week or so, officials say.

"Preliminary data did not show the kind of response in younger children we'd hoped for in order to say a single dose would be sufficient," says CDC director Thomas Frieden. "But...if the data show a difference, we will reconsider our recommendations."

For now, he adds, the CDC is sticking with its earlier recommendations.

Dr. Anthony Fauci, director of the National Institute of Allergies and Infectious Diseases, points out that only 25 to 36 percent of children under 10 achieved an antibody level considered protective against the new H1N1 virus.

But that was only 10 days after the first vaccine dose. The new data expected in early November will show what young children's antibody levels were three weeks after a single dose. It's possible they could be higher, Fauci says, but studies in adults didn't show much higher levels at 21 days than at 10 days.

Meanwhile, millions of US children will soon be due for their second dose of vaccine — and millions more haven't had their first dose because the vaccine has been in short supply. So it might be tempting to adopt the WHO's new recommendation.

But Fauci counsels caution.

"One of the dangers in jumping ahead and saying you want to stretch out the supply by giving a single dose to these young kids," Fauci says, "is that you'll be under-protecting them."

If that happened, he says, we wouldn't be saving a dose for each vaccinated child. We'd be wasting a dose.

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