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<Home> <Newsletter> <Third Issue> <Vaccine Safety> <One Dose of H1N1 Vaccine Immunogenic in High Percentage of Youth Ages 10 to 17>
VACCINE
SAFETY One Dose of H1N1 Vaccine Immunogenic in High Percentage of Youth Ages 10 to 17 Younger Children Likely Will Need Two Doses By David Mitchell
Kids and teenagers 10 years to 17 years old likely will need only one dose of vaccine to protect them against the novel influenza A (H1N1) virus. Younger children, however, probably will need two doses, according to preliminary data from a clinical trial sponsored by the NIH's National Institute of Allergy and Infectious Diseases, or NIAID.
Initially, public health officials had thought that children and adults would need two doses of H1N1 vaccine. However, the FDA said Sept. 15 that a high percentage of adults ages 18 to 64 years had a robust immune response to a single 15-microgram dose of nonadjuvanted vaccine. The vaccines used in the adult clinical trials were manufactured by CSL Ltd., based in Melbourne, Australia, and Sanofi Pasteur Inc., (2-page PDF; About PDFs) based in Swiftwater, Pa. Fauci said similar results seen with Sanofi Pasteur's H1N1 vaccine for children ages 10 to 17 years represented good news in terms of vaccine supply and efficacy. Results were not as favorable, however, in younger children. A strong immune response was reported in 36 percent of kids 3 years to 9 years of age who received single 15-microgram dose of the H1N1 vaccine and in only 25 percent of children 6 months to 35 months old who received one such dose. Fauci said the varying results were not unexpected and were similar to what typically is seen with administration of seasonal flu vaccine. Younger children, he said, have less mature immune systems and less prior exposure to flu viruses and, therefore, are unable to mount as great an immune response to a single vaccine dose. He said immune response likely would increase in all age groups closer to 21 days after vaccination. Younger children have been among those hardest hit by the H1N1 outbreak. Anne Schuchat, M.D., director of the CDC's National Center for Immunization and Respiratory Diseases, said during the Sept. 21 briefing that there have been at least 47 pediatric deaths linked to the novel virus. Children ages 6 months to 4 years and those ages 5 years to 18 years who have chronic medical conditions are among the groups identified as being at high risk for flu complications and prioritized to receive H1N1 vaccine. Although the NIAID trial is ongoing, Fauci said children ages 6 months to 9 years likely will need two H1N1 doses 21 days apart. Two doses also are recommended (1-page PDF; About PDFs) for children younger than age 9 years who are receiving seasonal influenza vaccine for the first time, which means some children will need a total of four flu immunizations this season. Healthy children ages 2 and older can receive live attenuated influenza vaccine, or LAIV, as a nasal spray. Jay Butler, M.D., chief of the CDC's H1N1 vaccine task force, said in a Sept. 18 media briefing that approximately 3.4 million doses of LAIV will be the first H1N1 vaccine distributed in early October. Fauci said Sept. 21 that no data are available yet from clinical trials of the LAIV version of H1N1 vaccine, but Jesse Goodman, M.D., the FDA's acting chief scientist, noted during the same briefing that efficacy and dosing results are expected to be similar to those seen with use of the inactivated vaccine. Although no severe adverse events have been reported in the H1N1 vaccine trials to date, no data have been released yet from sequential trials examining whether seasonal and H1N1 vaccines should be administered at the same time, said Fauci. However, Schuchat said that inactivated seasonal flu vaccine and inactivated H1N1 vaccine likely can be administered on the same day via injections in different arms. She said it is not advisable, however, to administer the nasal spray versions of both seasonal and H1N1 vaccines on the same day. Although H1N1 vaccine has not yet been distributed, seasonal flu vaccine already is available, with more than 50 million doses distributed as of Sept. 18, according to the CDC. "Parents can start getting their children vaccinated now," Schuchat said. "They don't need to wait." Goodman said additional data from NIH and manufacturer trials will be available in the near future. Fauci added that preliminary results from a trial involving pregnant women are expected to be available in early October.
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NIAID
Director Anthony Fauci, M.D., said in a Sept. 21 media briefing that a
single 15-microgram dose of a nonadjuvanted vaccine against 2009 H1N1
influenza generated a robust immune response in 76 percent of 10- to 17-year-olds
eight to 10 days after immunization. 
