A higher-dose influenza vaccine than is currently recommended appears to be more immunogenic in the elderly, reported Dr. Wendy A. Keitel of Baylor College of Medicine, Houston, and her associates.
“For reasons unknown, vaccine efficacy among elderly persons has been variable. A progressive reduction in immune competence is described with increasing age, and reduced antibody responses to inactivated influenza vaccines have been noted in elderly persons,” the investigators said.
They assessed the immunogenicity of several doses of a 2002 U.S. vaccine formulation in 202 healthy subjects aged 65–88 years.
The subjects were randomly assigned to receive a single intramuscular injection of trivalent inactivated subvirion influenza vaccine containing 15, 30, or 60 mcg of hemagglutinin per strain, or a placebo injection. The usual recommended dose is 15 mcg.
One month later, mean titers of antibodies to all the viral strains showed significant increases that corresponded to increasing vaccine dose. The percentage of subjects who attained protective titers of antibodies also rose with increasing vaccine dose, the researchers said (Arch. Intern. Med. 2006;166:1121–7).
Among subjects who had the lowest antibody titers at baseline, the antibody response to the 60-mcg dose was nearly double that to the 15-mcg dose of the vaccine.
All vaccine doses were deemed safe and well tolerated. There were significant dose-related rises in the frequencies of injection-site pain and redness or swelling, but most of these reactions were mild and transient.
There were no dose-related differences in systemic symptoms and no serious adverse events attributed to the vaccines.
Further, larger-scale trials are warranted to confirm the finding that enhanced-potency vaccines are safe and effective in the elderly, Dr. Keitel and her associates said.
The vaccines for this study were provided by the drug manufacturer Aventis Pasteur.