More effective influenza vaccine

May 3 2006

An intranasal influenza vaccine proved to be more effective than the injectable influenza vaccine in children older than 6 months and younger than 5 years of age, according to study data presented at the annual meeting of the Pediatric Academic Societies in San Francisco.

The results point to a new way of looking at how to best protect very young children from various influenza strains, said Robert Belshe, M.D., a Saint Louis University researcher who is presenting the results today.

"We tested this needle-free vaccine in more than 8,000 children at 249 sites in 16 countries," said Dr. Belshe, director of the Center for Vaccine Development at Saint Louis University School of Medicine. "We discovered that the intranasal vaccine was significantly more effective in protecting these children against influenza infection than the injectable flu shot. This is especially significant because this age group is among the most vulnerable to flu infection, and they tend to spread influenza around to other family members."

The data indicate that the intranasal vaccine candidate, known as CAIV-T (Cold Adapted Influenza Vaccine Trivalent), was 55 percent more effective than the injectable vaccine in reducing influenza-like illness in children.

This is the largest head-to-head influenza vaccine study ever conducted. The trial included nearly 8,500 children, with about half receiving the U.S. Food and Drug Administration (FDA)-approved injectable and the other half receiving the nasal spray influenza vaccine.

Belshe said influenza vaccine must be manufactured several months before the influenza season, so in some years there's a vaccine "mismatch" with the strain of flu that is circulating. This has happened four out of the last eight years. The study results also indicated that this nasal spray vaccine is more effective than shots against influenza A strains and also more effective in years in which the circulating strain of influenza is "mismatched" with that contained in the seasonal vaccine.

"The nasal spray vaccine showed high efficacy in years when epidemic flu viruses were not well matched to the recommended vaccine antigen," Belshe said. "This sort of broad protection from a live, attenuated intranasal vaccine suggests that this vaccine has properties that make it superior to the traditional flu shot."

FluMist. (Influenza Vaccine Live, Intranasal) is the only currently marketed live, attenuated, intranasal vaccination option for healthy children and adults between the ages of 5 and 49 years. CAIV-T is the investigational, next-generation, refrigerator-stable formulation of FluMist.

Study participants were randomized to receive either FluMist or the injectable influenza vaccine during the 2004-2005 influenza season. Each participant received a placebo nasal spray or placebo injection to preserve the double-blind design of the study. Participants also were followed through the influenza season and evaluated to identify illnesses caused by influenza virus. The trial included a record 6,384 previously unvaccinated children, with nearly 50 percent of those children less than 2 years of age.

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