IDSA: Fluzone Safe and Immunogenic in Infants Ages Six to 12 Weeks

TORONTO, Oct. 17 -- The Fluzone inactivated trivalent influenza vaccine, which is licensed for children older than six months and adults, is safe and immunogenic in infants from six and 12 weeks old, researchers reported here.

"Children less than six months of age have actually the highest rate of hospitalization and medically attended (influenza) illnesses of any age group, including the very old," said Janet Englund, M.D., of the University of Washington in Seattle.

"But there is no licensed vaccine for this age group," Dr. Englund noted during a symposium at the Infectious Diseases Society of America meeting.

With colleagues at 31 sites in the U.S., Dr. Englund conducted a randomized, double-blind prospective placebo-controlled trial to test the safety and immunogenicity of the Fluzone vaccine in healthy infants. The study took place during the fall of 2005 and the winter of 2006.

The babies were given an intramuscular injection of 0.25 milliliters of vaccine or placebo between the ages of six and 12 weeks, in conjunction with standard pediatric vaccines. They were given another injection of the same amount of drug or placebo four weeks later, Dr. Englund reported.

All told, 915 babies were randomized to the vaccine arm and 460 to placebo, she said. Blood was drawn at four and seven months of age to determine antibody titers.

The vaccine included two influenza A strains and one B strain, Dr. Englund said, and after the second injection, geometric mean titers of antibodies to all three were significantly higher (at P<0.001) for babies who got the vaccine compared to those on placebo.

The proportion of babies with potential seroprotection -- an antibody titer of at least 1:40 -- was significantly higher (again at P<0.001) in the vaccine arm than in the placebo group for each flu strain.

About 11% of infants in each study group had a fever greater than 38C within three days of the first injection -- given concurrently with other vaccines -- and about 3% in each group after the second shot, Dr. Englund said.

There was also no significant difference between arms in rates of such reactions as irritability, vomiting, abnormal crying, or injection site reactions, she said.

Serious adverse events were similar between the arms and only one -- a hypersensitivity reaction that occurred within 30 minutes of a Fluzone dose -- was considered to be related to the study drug. The child was not hospitalized.

"Certainly, children younger than six months have high morbidity and at the moment we have nothing to offer them for protection," said Kathleen Neuzil, M.D., also of the University of Washington and senior clinical advisor for vaccines for PATH, a Seattle-based nonprofit international health advocacy organization.

She noted that the immune response seen in infants in the study "isn't as good as in older children, but it's better than nothing and what we're doing right now is nothing."

But the important thing about the finding is that "even if you're only getting a moderate benefit, it's safe," Dr. Neuzil said.

The vaccine is manufactured by Sanofi Pasteur.