By Rob Stein
Washington Post Staff Writer
Tuesday, September 22, 2009
Most older children appear to need just one dose of the new swine flu vaccine, but younger ones will probably require two, federal health officials reported Monday.
Preliminary results from tests involving about 600 subjects ages 6 months to 17 years found that 76 percent 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 of babies age 6 months to 35 months, and 36 percent of kids ages 3 to 9, had a strong response, indicating that they will need two shots.
The findings mark the second piece of good news about the swine flu vaccine. Officials reported Sept. 10 that most adults would probably need only one shot, despite expectations that all ages would need two doses to fully prime them 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 government efforts to develop the vaccine.
Unlike the usual seasonal flu, which tends to hit the elderly hardest, the swine flu virus, known as H1N1, tends to infect children and young adults more commonly. The rate of infections has been highest among people 5 to 24 years old.
The government is testing vaccine made by Sanofi Pasteur in Swiftwater, Pa., one of five companies producing vaccine for the United States. One study compared two injections of 15 micrograms of vaccine to two injections of 30 micrograms three weeks apart in 650 subjects in Baltimore; Durham, N.C.; Kansas City, Mo.; Nashville; and Seattle.
Officials believe, based on the results of blood tests eight to 10 days after the first shots, that one standard 15 microgram dose will be sufficient for older children. But younger children who have never had a flu shot will most likely need one dose followed by a booster, meaning they will need a total of four flu shots this year -- two for the seasonal flu, and two about 21 days apart to protect against the swine flu.
"This is going to be a complicated flu season," said Anne Schuchat of the Centers for Disease Control and Prevention.
Although data are not yet available for the new FluMist nasal spray, officials said they expect similar findings for that vaccine.
So far all the vaccines appear safe, officials said.
"There have been no serious adverse events," Fauci said.
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 CDC.
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.
"This is during a period of time when we usually would see zero children dying from influenza," Schuchat said.
As a result, people between the ages of 6 months and 24 years are among those getting priority for the vaccine.
Although the virus appears to be causing relatively mild disease so far, experts think that many more people will become 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 that as many as 90,000 people could die this year because of H1N1.
In response, federal, state and local health officials are rushing to prepare 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 more than 250 million doses of vaccine -- and perhaps enough to inoculate every American -- for the most ambitious vaccination campaign in U.S. history. The first doses are expected to become available in October, and many schools are planning to offer the shots to students.