Enhance the national influenza vaccination strategy

August 2005

In their commentary, David S. Fedson, MD, and Kristin Nichol, MD, MPH, claim that the article by Simonsen and colleagues, published jointly by researchers at the National Institutes of Health and Entropy Research Institute (ERI), questions the benefits of annual influenza vaccination for the elderly.

That claim is a misinterpretation of the conclusions of the article. It is clear from many observational studies that there is a benefit to influenza vaccination for some elderly people, and this was acknowledged in the discussion in the article. However the principal finding of the article was the demonstration that over a 20-year period, despite a more than threefold increase in influenza vaccine coverage, no progress at all was made toward the stated objective of the national vaccination program, namely a reduction in influenza-attributable mortality in the U.S. population, ages 65 and over.

We suggest, in the article, that to overcome this lack of progress, the national strategy should be enhanced. Evidence from studies of multiple types indicates that significant reductions of mortality in the elderly as a whole can be achieved by expanding the vaccination program to include not only risk groups, but also transmission groups, specifically schoolchildren.

Fedson and Nichol imply that the results of observational studies on selected populations represent all community-dwelling elderly; that these are a homogenous population that is 95% of all elderly; and that population-based results, such as those in the article, distort the picture relevant to nearly all elderly by the inclusion of groups, such as those dwelling in nursing homes. However, the sample of many observational studies, specifically home maintenance organization subpopulations of community dwellers, is well known to be in better health than, and poorly representative of, the heterogeneous population of community dwellers.

If one-third of all deaths occurred among the nursing home subpopulation and the remaining two-thirds occurred among a homogenous subpopulation of community dwellers, increasing vaccine coverage from 20% to 65% (as was done in the United States between 1980 and 1999) should have reduced the winter mortality for community dwellers by 22.5% (50% effectiveness x 45% change in coverage) and the total winter mortality for the population by 15% (22.5% of 2/3). This level of reduction would have all but eliminated the historical winter peak in all-cause mortality for the entire population (never more than 20% of all deaths), ages 65 and over. This did not occur, for any age group, not even among the younger elderly population, a fraction of whom live in institutions. Therefore, it is clear that the sample populations of observational studies cannot be extrapolated to the population of community-dwelling elderly, ages 65 and over.

A recent study performed at ERI used national mortality data from three countries: Australia, Canada and France. The populations of these countries differed in their constituent racial, ethnic and social groups. Their health care systems were quite different from that in the United States. However, the national programs of vaccination were, as in the United States, also focused only on high-risk groups, and we found the same result as we did in the United States, namely no change in excess mortality for any elderly population age group. The only national vaccination program that has produced a decrease in excess mortality in the elderly population on a national basis was the schoolchildren vaccination program in Japan. An enhanced strategy will be critically important in the event of a pandemic when vaccinating those who are most likely to spread the disease will have a multiplier effect in reducing total population deaths. Results from studies on selected subpopulations that cannot be extrapolated to the total population to be protected must not distract us.

For more information:

• Fedson DS, Nichol KL. Should we question the benefits of influenza vaccination for the elderly? IDN. 2005;18(8):6-8.
• Keppel KG, Pearcy JN. Healthy People 2000: an assessment based on the health status indicators for the United States and each state. Hyattsville, MD: National Center for Health Statistics; 2000:1-31.
• Monto AS, Davenport FM, Napier JA, et al. Modification of an outbreak of influenza in Tecumseh, Michigan by vaccination of schoolchildren. J Infect Dis. 1970;122(1):16-25.
• Piedra PA, Gaglani MJ, Kozinetz CA, et al. Herd immunity in adults against influenza-related illnesses with use of the trivalent-live attenuated influenza vaccine (CAIV-T) in children. Vaccine. 2005;23(13):1540-1548.
• Reichert TA, Hampson A, Tam T, et al. National vaccination programs for the control of influenza: No evidence of a reduction in excess mortality in four countries (A report from the MISMS study). 2005. In Press.
• Simonsen L, Reichert TA, Viboud C, et al. Impact of influenza vaccination on seasonal mortality in the US elderly population. Arch Intern Med. 2005;165(3):265-272.
• Weycker D, Edelsberg J, Halloran ME, et al. Population-wide benefits of routine vaccination of children against influenza. Vaccine. 2005;23(10):1284-1293.
• Thomas A. Reichert PhD, MD, and Ronald A. Christensen PhD, JD, are with Entropy Research Institute in Lincoln, Mass.