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Mixed Results of Swine Flu Vaccine in Kids

Early results from clinical trials suggest that healthy children under the age of 9 will likely need two doses of the swine flu vaccine, but those between 10 and 17 can get by with a single shot, U.S. health officials announced today.

In studies sponsored by the U.S. National Institute of Allergy and Infectious Diseases (NIAID), 8 to 10 days after receiving a 15 microgram dose of an inactivated vaccine that contains proteins from the novel H1N1 virus, 76% of the older children had a “robust” antibody response. But in those children between 3 and 9 years old, the same immune response was only seen in 39% of vaccinated kids, and it dropped to 25% in children 6 to 35 months. Anthony Fauci, head of NIAID, stressed at a press conference that the vaccine behaves very much like the seasonal flu vaccine, which similarly requires a second dose in younger children because of their less mature immune systems. “Overall, this is very good news for the vaccination program, both in regard to supply of vaccine as well as to its potential efficacy,” Fauci said.

As Fauci explained, researchers expect antibody responses to continue to climb for up to 21 days, the end points of the studies. The trials, which involve 600 children, found no important differences in antibody responses to 15 micrograms or 30 micrograms of the vaccine. The percentage of people who have a robust antibody response indicates whether a second dose is needed, but no strict cut off exists, and recommendations may change if conflicting data surface before the vaccine becomes widely available in mid-October. The results from the older children closely match early results seen with novel H1N1 vaccine in adults. None of the studies have reported serious side effects.

A small amount of the vaccine will become available in early October for people determined to be at high risk of suffering severe disease from the novel H1N1 virus, but that will be a live, attenuated product. No data yet exist about the efficacy of that swine flu vaccine, although Jesse Goodman of the U.S. Food and Drug Administration said at the press conference that “it is likely that younger children may need a second dose.”

In what clearly will pose a logistical challenge for both parents and healthcare providers, younger children will ideally receive two doses of the seasonal flu vaccine, spaced 21 days apart, and also two doses for swine flu. Anne Schuchat, head of the National Center for Immunization and Respiratory Diseases at the U.S. Centers for Disease Control and Prevention, said the inactivated seasonal and swine flu vaccines can be given simultaneously, but there are concerns about giving both versions of the inactivated and live products at the same time. She advised parents of younger children to start giving them the seasonal vaccine, which is widely available, now. “This is going to be a complicated flu season,” said Schuchat.