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.

For more information on influenza see http://www3.niaid.nih.gov/news/focuson/flu. Also visit http://www.PandemicFlu.gov for one-stop access to U.S. Government information on avian and pandemic flu.

NIAID is a component of the National Institutes of Health, an agency of the U.S. Department of Health and Human Services. NIAID supports basic and applied research to prevent, diagnose and treat infectious diseases such as HIV/AIDS and other sexually transmitted infections, influenza, tuberculosis, malaria and illness from potential agents of bioterrorism. NIAID also supports research on transplantation and immune-related illnesses, including autoimmune disorders, asthma and allergies.

The National Institutes of Health (NIH) -- The Nation's Medical Research Agency -- includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.
Reference: W Keitel et al. Safety of high doses of influenza vaccine and effect on antibody responses in elderly persons. Archives of Internal Medicine DOI: 10.1001/archinternmed.166.10.1121 (2006).

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