Children ages 10 to 17, who are among those facing the greatest risk from the swine flu, appear to need just one dose of the new vaccine, but younger children will probably need two, federal health officials reported Monday.
Preliminary results from tests involving about 600 subjects ages 6 months to 17 years found that 76 percent of those age 10 and older who received a standard single shot experienced a strong enough response within eight to 10 days to assume they would be protected. But only 25 percent to 36 percent of the younger children had a strong response, indicating that they will need two shots.
The findings mark the second piece of good news about the new swine flu vaccine. Officials reported Sept. 14 that adults would probably need only one shot, despite expectations that all ages would need two doses in order to prime the immune system against a new virus.
“Overall, this is very good news for the vaccination program, both in regard to supply of the vaccine as well as its potential efficacy,” said Anthony S. Fauci of the National Institute of Allergy and Infectious Diseases, which is leading the government’s efforts to develop the vaccine.
Unlike the usual flu, which tends to hit the elderly hardest, the H1N1 virus tends to infect children and young adults more commonly. The rate of infections has been highest among people ages 5 years to 24 years, followed by babies younger than 5.
The government is testing a vaccine made by Sanofi Pasteur in Swiftwater, Pa., one of five companies producing vaccines for the United States. One study compared two injections of 15 micrograms of vaccine with two injections of 30 micrograms three weeks apart in 650 subjects in Baltimore, Nashville, Durham, N.C., Kansas City, Mo., and Seattle.
Based on the findings, officials expected that younger children, who have never been exposed to a flu virus, will need a total of four flu shots this year — two for the regular seasonal flu vaccine and two about 21 days apart to protect against the swine flu. Although data are not yet available for the new FluMist nasal spray flu vaccine, officials said they expected similar findings for that vaccine. So far the vaccine appears safe, officials said.
“There have been no serious adverse events,” Fauci said.
A second study is examining the safety of administering 15 micrograms of swine flu vaccine at the same time as the seasonal flu vaccine among 650 subjects in St. Louis, Atlanta, Cincinnati, Houston, Iowa City and Galveston, Tex. Those results were not yet available, but officials recommended parents go ahead and get their children vaccinated as soon as both vaccines are available.
At least 21 states, including Maryland and Virginia, are experiencing widespread flu activity, which is highly unusual this early in the year, according to the federal Centers for Disease Control and Prevention.
More than 296,471 laboratory-confirmed swine flu cases among all ages have been reported to the World Health Organization and at least 3,486 deaths have occurred worldwide, including at least 364 in the United States. About one in every 13 U.S. deaths have been in children and at least 47 children have died from the swine flu so far this year.
“This is during a period of time when we usually would see zero children dying from influenza,” said the CDC’s Anne Schuchat.
As a result, people between the ages of 6 months and 24 years are among those getting priority for the vaccine, along with pregnant women, people who live with or care for children younger than 6 months of age, health-care and emergency medical services personnel, and people ages of 25 through 64 years of age who are at higher risk because of chronic health disorders or weak immune systems.
Although the virus appears to be causing relatively mild disease so far, experts expect many more people will get infected because most have no immunity against it. Flu contributes to about 36,000 deaths each year in the United States, but a presidential panel estimated as many as 90,000 could die this year because of H1N1.
In response, federal state and local health officials are rushing to prepare for the pandemic, including making a variety of emergency plans to cope with a surge of people who are sick or think they are sick, which could overwhelm the health-care system.
The federal government is buying at least 195 million doses of vaccine — and perhaps enough to vaccinate every American — for the most ambitious vaccination campaign in U.S. history. The first vaccine is expected to become available in October, and many schools are planning to offer the shots to students.
