Data show swine flu vaccine’s potency

Federally funded studies also affirmed that children age 9 and younger will need two doses of vaccine to produce a strong enough response by their immune systems to protect them against the H1N1 virus, officials reported.

“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 the swine flu virus, which is circulating widely 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.

In the new results, an analysis of samples from 50 pregnant women in their second or third trimesters taken 21 days after they received a standard dose of vaccine found that 92 percent experienced a sufficient response to assume they would be protected.

“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.

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.

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.