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More Evidence for Herd Protection of the Elderly

Amesh A. Adalja, MD, FACP, FACEP, FIDSA, September 18, 2015

Herd protection is a real phenomenon that has great potential to change the face of vaccine-preventable diseases. Vaccines have cascading benefits and a well-vaccinated society, in which vaccine-preventable diseases are minimized, is ideal. The benefits of vaccine-induced herd immunity have been well established for measles and now pneumococcus as discussed in the 9/4/2015 CBN. Most recently, a study published in Clinical Infectious Diseases shows the benefit of influenza vaccination of younger adults on preventing influenza in the elderly.


Benefit of non-elderly adult vaccination

Tasker and his Cleveland Clinic colleagues queried several databases for influenza vaccination rates of urban counties between the years 2002-2010. The data set analyzed amounted to over 300 counties that account for 56.6% of the US population. Just 55.4% of the elderly had a documented influenza vaccine

The striking finding of the study was that as vaccine coverage of younger adults (age 18-64) in a county increased from less than 15% to greater than 31%, the odds of an elderly individual in that county contracting influenza diminished by 20%, as did pneumonia rates. This benefit was more apparent in the unvaccinated elderly.


Implications for immunization efforts, pandemic plans

This study reinforces the importance of universal immunization of all age groups. Prior studies have shown the impact of vaccinating children against influenza on elderly adults and now Tasker and colleagues have shown that benefit is not limited just to children. Also, the fact that those who benefit most are the unvaccinated elderly underscores the need to maximize vaccination rates in that group. However, as influenza vaccine is known to be less effective in the elderly, increased community-wide influenza vaccine rates would be optimal. Lastly, aspects of pandemic influenza planning, as Tasker and colleagues note, include near-universal vaccination of children and young adults. The findings of this new study suggest that given the much lower vaccination rates typically seen, vaccination of non-elderly adults (with whom the elderly have more contact) may be especially important. This should inform future pandemic plans as vaccinating all non-elderly adults will contribute to societal resiliency.



Tasker GB, Rothberg MB, Culter DM. Association of influenza vaccine coverage in younger adults with influenza-related illness in the elderly. Clin Infect Dis 2015. Accessed September 15, 2015.