Pregnant? One dose of H1N1 vaccine works

Pregnant women need only one dose of vaccine to protect them from H1N1, according to government data released Monday that confirm what officials have been recommending.

Federally funded studies also affirmed that children 9 and younger will need two doses of vaccine to produce a strong enough response by their immune systems to protect them against the virus, officials said.

The findings came as an independent panel of experts organized by the Health and Human Services Department to monitor the safety of the vaccine met for the first time to review the data. "No safety concerns have arisen," said Anthony Fauci of the National Institute of Allergy and Infectious Diseases, which has been leading the government's efforts to test the vaccine.

The government has begun an unprecedented campaign to inoculate millions of Americans against H1N1, which is circulating in nearly all states. The program, however, has gotten off to a slower start than officials had hoped, with only about 30 million doses available, causing frustration and anxiety as long lines have formed at clinics nationwide.

92 percent showed a response

In the new results, an analysis of blood samples from 50 pregnant women in their second or third trimesters taken 21 days after they received a 15-microgram dose of vaccine found that 92 percent experienced a sufficient response to assume they would be protected. Although 96 percent of those who received a 30-microgram dose experienced a similarly strong response, officials concluded that the 15-microgram dose being used as a standard was sufficient.

"This should be reassuring news for those women who have already received the vaccine, and it is vital information for those women who have not been vaccinated," Fauci said.

Previous results showed that most other adults also need only one shot.

For kids, a booster is key

Additional data from blood tests on 583 children, however, found that only 25 percent of those ages 6 months to 35 months and only 55 percent of those ages 3 to 9 years had a strong enough immune response to protect them 21 days after getting only one shot. But 100 percent of the young children and 94 percent of those ages 3 to 9 experienced a strong enough response eight to 10 days after a booster.

Children in this age group also typically require two doses of the seasonal flu vaccine the first time they are immunized because they retain no residual immunity from earlier infections or vaccinations.

Fauci emphasized that the only adverse events reported in any of the clinical trials have been redness and swelling of the arm, typical of all vaccinations. Although one death has been reported among people who received the immunization, that person died from the flu, not the vaccine, said Bruce Gellin, who heads the National Vaccine Program Office.

The Los Angeles Times contributed to this report.