Higher dose of flu vaccine improves immune response in the elderly

May 23 2006

There may be a simple way to provide elderly Americans with extra protection against the annual flu virus: give them a higher dose of seasonal flu vaccine.

This idea is suggested by the results of a newly reported clinical trial supported by the National Institute of Allergy and Infectious Diseases (NIAID).

The trial, described in the latest issue of the Archives of Internal Medicine, was conducted by a team of researchers from Baylor College of Medicine in Houston, TX, and sanofi pasteur, the vaccines business of the sanofi-aventis Group in Paris. Led by Dr. Wendy Keitel, M.D., the team conducted the trial at the Baylor Vaccine and Treatment Evaluation Unit, which is one of a network of NIAID-supported sites at university research hospitals across the United States that conduct Phase I and II clinical trials to test and evaluate candidate vaccines for infectious diseases.

NIH Director Elias A. Zerhouni, M.D., notes, "The study results reported by Dr. Keitel and her colleagues are important because they suggest that a higher dose of seasonal influenza vaccine can safely and significantly increase the immune responses of older people."

"Elderly Americans are among the most vulnerable to serious complications of influenza because they generally have more underlying diseases and weaker immune systems than younger people," says NIAID Director Anthony S. Fauci, M.D. "These findings are an important first step in developing new strategies to better protect the elderly against influenza-associated hospitalizations and mortality."

"If you look at people who are dying and going into the hospital during an outbreak of seasonal influenza," says Dr. Keitel, "the majority of those people are older individuals."

Influenza accounts for some 36,000 deaths and more than 200,000 hospitalizations every year in the United States. It is among America's most lethal killers simply because the virus infects so many people--some 5 to 20 percent of the U.S. population every year.

In other influenza vaccine studies, higher antibody levels resulted in better protection against infection. Conversely, decreased antibody production in the elderly can leave them more susceptible to infection and the severe complications of influenza. Helping elderly people increase antibody production should help them fight off influenza infections, and this is exactly what Dr. Keitel and her colleagues set out to test when they began the clinical trial. They hypothesized that elderly people could be given higher doses of vaccine safely and that these higher doses would increase the antibody response and confer increased protection without increasing side effects.

In the study, the investigators randomly assigned 202 adults 65 years of age or older into four equal-sized groups: those receiving the normal dose of vaccine (15 micrograms); twice the normal dose (30 micrograms); four times the normal dose (60 micrograms); or a placebo. The average age of the volunteers was 72.4 years. All study participants were followed for a month post-vaccination to look for any vaccine-related side effects and to collect blood to evaluate antibody responses.

Dr. Keitel and her colleagues found that participants in the high-dose group (60 micrograms) had 44 to 79 percent higher levels of antibody than did those who received the normal dose of vaccine. Higher doses also increased the number of elderly volunteers achieving levels of antibody that have been associated with protection against influenza. Moreover, the vaccine was well-tolerated at all dosage levels. Although the higher doses of vaccine caused more mild side effects at the injection site, there were no significant differences in systemic symptoms such as fever or body aches among the groups.

The successful achievement of higher levels of antibodies in this study suggests that larger doses of vaccine may be a safe and viable way of enhancing protection against influenza among elderly persons. These promising results provide a basis for further evaluation of enhanced potency vaccines in the elderly, says Dr. Keitel.