Senior man coughing while wife pats his back
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Influenza and respiratory syncytial virus pose substantial mortality risk to U.S. seniors, according to the first study of excess deaths for the two diseases since 2009.

The study also highlighted the long-lasting seasonal impact of the 2009 H1N1 influenza pandemic on seniors’ flu outcomes.

Researchers investigated excess age- and region-specific mortality in the United States between 1999 to 2018 using data from death certificates. The prevalence of H1N1 in flu season appeared to help determine whether RSV or flu would have the upper hand, reported study lead Cécile Viboud, Ph.D., of the National Institutes of Health, and colleagues. 

Flu deaths determined by seasons’ top virus

Image of Cécile Viboud, Ph.D.; Image credit: NIH
Cécile Viboud, Ph.D.; Image credit: NIH

The results revealed a significant decrease in the number of excess influenza deaths among adults aged 65 years or older since 1999. This age group accounted for 75% of excess flu deaths during the study period compared to 90% of excess flu deaths prior to 1999. 

Investigators attributed this change to the increased use of the highly protective influenza vaccine Fluzone High-Dose licensed in 2009 for use in older adults, and stable vaccination rates over time. In addition, the emergence of influenza A/H1N1 during the 2009 flu pandemic has shifted mortality toward middle-aged adults. Many older adults have had early-life exposure to similar viruses, likely shielding them from severe disease, Viboud and team explained. 

But they also found large seasonal fluctuations for flu mortality each year, with rates among the elderly rising when influenza A/H3N2 is the dominant virus. 

RSV testing could help lower high mortality rates

Excess RSV mortality, meanwhile, was highest among the 65-and-older age group during the study period. And in seasons when H1N1 is dominant, it was associated with more deaths than flu, the researchers found. 

Unlike the findings for flu, annual RSV mortality was less variable by season but more so by geographical location. The South Central region had the highest mean rates, while the Pacific Northwest had the lowest, investigators reported.

Despite RSV’s substantial association with mortality in seniors, testing for the virus is not widespread, the authors noted. The study results may provide a benchmark to help clinicians and other stakeholders evaluate respiratory virus interventions, including new or improved immunization strategies, they concluded.

“A better understanding of RSV testing practices is an important area for future work given recent changes and would provide further evidence to support recommendations for an RSV vaccine and monoclonal antibody products soon to be licensed,” they wrote.

Full findings were published in JAMA Network Open.

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