Influenza vaccinations don’t reduce flu-related mortality rates in elderly adults in the United States, and prior reports of the vaccine’s efficacy in this population have been exaggerated, according to a report published Sept. 24 in the Lancet Infectious Diseases.

Although flu vaccination rates in the United States have increased from 15% to 65% since 1980, recent mortality studies cannot confirm any decrease in flu-related deaths in adults aged 70 years and older, wrote Lone Simonsen, Ph.D., of George Washington University, Washington, and colleagues (Lancet Infect. Dis. 2007 [Epub doi:10.1016/S0140-6736(07)61389-0]).

To assess the validity of the evidence for and against flu shots for the elderly, the researchers reviewed data from previous studies and found few randomized, controlled trials of flu vaccination effectiveness in the elderly Most of the current evidence stems from observational studies that compared mortality rates in vaccinated vs. unvaccinated persons.

 In addition, studies of flu vaccination and flu-related mortality in the elderly likely are affected by selection bias and don’t account for frailty, the researchers explained. The review included all available clinical studies of vaccine effectiveness in elderly persons. Of note, data from the largest and most rigorous placebo-controlled randomized study (which is often cited as evidence of vaccine effectiveness) showed that the flu vaccine’s effectiveness may decline with age. The study, which included 1,838 healthy adults aged 60 and older, cites a 50% vaccine efficacy among adults aged 60 and older, the researchers noted (JAMA 1994;272:1661-5). But vaccine efficacy was only 23% among adults aged 70 years and older, compared with 57% among persons aged 60-69 years.

The decline in flu vaccine benefits is consistent with evidence of a decline in overall immune responsiveness later in life. The researchers cited data from a review of placebo-controlled antibody responses showing that responses of older persons receiving the vaccinations were one-quarter to one-half as vigorous as responses in younger adults, although data are limited for persons aged 70 years and older (Vaccine 2005;24:1159-69). More research is needed to evaluate the potential benefits of flu vaccination for the elderly, but the study designs need work. “It may be necessary to abandon cohort studies that rely solely on electronic databases in favor of case-control studies with laboratory-confirmed endpoints,” the researchers said.