"We found the vaccine delivered good antibody responses, whether it was given through nose drops or the nasal spray," says Dr. King, the principal investigator of the study. "It proved not only to be safe but much more accepted by children because they did not need to have a flu shot."
Although most people who receive flu vaccinations are adults, children with chronic diseases such as asthma also routinely receive flu shots. If more children could receive this type of protection against the flu, it could help stop the spread of the disease in the rest of the community, according to Dr. King.
"Children can easily spread the flu virus. If we can prevent them from getting sick, we may have a profound impact in breaking the chain of transmission." Dr. King adds that the new vaccine potentially could be offered to adults in the future.
Influenza is the leading viral killer in the U.S. The flu also has a significant economic cost, estimated in the billions of dollars per year in doctor visits and days lost from work, according to Dr. King.
The study included 356 children between the ages of 18 months and six years, who received the nasal vaccine or a placebo. The vaccine contained three live, weakened influenza virus strains that stimulate antibodies, which the body uses to fight the infection. The study, which lasted from the fall of 1995 to the spring of 1996, was conducted at four sites in the U.S. and at one in Chile.
Blood samples were taken before the children received the vaccine and again 42 days later to check for antibody levels. Results showed good antibody response to two of the three strains. The results were the same whether the vaccine was administered as a nasal spray or as nose drops. While antibody levels were less than expected in the third strain, Dr. King believes those levels would increase if children were to receive two doses of the flu vaccine several weeks apart. A larger study to confirm that is underway.
That study, to examine the effectiveness of two doses of the nasal vaccine, has been conducted in 1300 children at the University of Maryland Medical Center and at nine other sites across the United States this year. Researchers are just beginning to analyze the data and Dr. King says they should have a better picture of how well the vaccine protects children from influenza by this fall. If the new vaccine, in nose drop or nasal spray form, proves to be effective and wins FDA approval, it could be on the market starting in 1999.
The research was funded by the National Institute of Allergy and Infectious Diseases (NIAID) in partnership with Aviron, a Mountainview, California company that manufactures the vaccine. The earlier study, led by Dr. King, was conducted at NIAID vaccine evaluation units at the University of Maryland Medical Center, Baylor College of Medicine in Houston, St. Louis University in St. Louis, Cincinnati Children's Hospital in Cincinnati, and at the Hospital Roberto Del Rio in Santiago, Chile.