Higher flu Vaccine Doses Improve Antibody Responses in Elderly

Immunization against influenza has been very effective in preventing disease in all age-groups, except the elderly-the very group that is most susceptible to the worst outcomes, including hospitalization and death.

Arch Intern Med

Newly published evidence suggests that higher-dose vaccines produce significantly higher serum antibody levels and are generally safe in this population (. 2006;166: 1121-1127).

Some 202 ambulatory adults aged ≥65 years were randomized to a single intramuscular injection of trivalent inactivated influenza vaccine containing the standard amount of antigen (15 µg of hemagglutinin per strain), 2 to 4 times greater amounts of antigen (30 or 60 µg of hemagglutinin per strain), or placebo.

At 30 days after immunization, the higher the dose, the better were the serum antibody level, the antibody response, and the protective titer.

In the group given the 60-µg dose, mean serum hemagglutination inhibition against the 3 virus strains contained in the vaccine were 44% to 71% higher, and neutralizing antibody levels were 54% to 79% higher, than in the group given the standard 15-µg dose.

Among participants whose initial antibody titers fell within the lower half of the antibody range, the 60-µg dosage resulted in almost twice as many antibody responses compared with the standard 15-µg dosage.

“The dose was the most important factor associated with an improved antibody response,” write Wendy A. Keitel, MD, of Baylor College of Medicine, Houston, Tex, and colleagues.

While there were dose-related increases in the frequency of injection site reactions, all the doses used were well tolerated.

The investigators did not test doses higher than 60 µg, explaining that, “The increased doses tested in this study were selected because they would not significantly affect projected future vaccine supply.” The results of this study, they added, should encourage further investigation into the use of enhanced-potency vaccines for older individuals.

Each year, influenza epidemics cause more than 50,000 deaths and almost 300,000 hospitalizations in the United States, primarily in persons older than 65 years.