As a comparison, national coverage with influenza vaccines for all U.S. adults was 48.3% in the same time period—2% higher than the past year.
The cohort study led by researchers from the CDC in Atlanta involved 7,998 hospitalized adults in 20 U.S. states between February 2022 and May 2023.
“These findings suggest that before RSV vaccine introduction in the U.S., RSV disease was at least as severe as COVID-19 or influenza among unvaccinated patients and more severe than COVID-19 or influenza among vaccinated patients hospitalized with those diseases,” the authors advised.
The CDC recommended the first RSV vaccines on June 21, 2023, for adults aged 60 years and older using shared clinical decision-making. “Understanding the severity of RSV disease in adults can help guide this clinical decision-making,” according to the report in the Journal of the American Medical Association Network Open.
The study sought to describe disease severity among adults hospitalized with RSV and compare it with the severity of COVID-19 and influenza disease by vaccination status. To do that, the research team prospectively enrolled adult participants who had been admitted to the hospital with acute respiratory illness and laboratory-confirmed RSV, SARS-CoV-2, or influenza infection at 25 hospitals in 20 states from February 1, 2022, to May 31, 2023. The 7,998 participants had a median age of 67 years and 50.6% were female. Data were analyzed from August 2023 to October 2023.
The researchers used multivariable logistic regression to compare the severity of RSV disease with COVID-19 and influenza severity, by COVID-19 and influenza vaccination status, for a range of clinical outcomes, including the composite of invasive mechanical ventilation (IMV) and in-hospital death.
Of the participants, 484 (6.1%) were hospitalized with RSV, 6422 (80.3%) were hospitalized with COVID-19, and 1092 (13.7%) were hospitalized with influenza.
The results indicated that, among patients with RSV, 58 (12.0%) experienced IMV or death, compared with 201 of 1,422 unvaccinated patients with COVID-19 (14.1%) and 458 of 5,000 vaccinated patients with COVID-19 (9.2%), as well as 72 of 699 unvaccinated patients with influenza (10.3%) and 20 of 393 vaccinated patients with influenza (5.1%).
“In adjusted analyses, the odds of IMV or in-hospital death were not significantly different among patients hospitalized with RSV and unvaccinated patients hospitalized with COVID-19 (adjusted odds ratio [aOR], 0.82; 95% CI, 0.59-1.13; P = .22) or influenza (aOR, 1.20; 95% CI, 0.82-1.76; P = .35); however, the odds of IMV or death were significantly higher among patients hospitalized with RSV compared with vaccinated patients hospitalized with COVID-19 (aOR, 1.38; 95% CI, 1.02-1.86; P = .03) or influenza disease (aOR, 2.81; 95% CI, 1.62-4.86; P <.001),” the authors wrote.
The study concluded that, among adults hospitalized in this U.S. cohort during the 16 months before the first RSV vaccine recommendations, “RSV disease was less common but similar in severity compared with COVID-19 or influenza disease among unvaccinated patients and more severe than COVID-19 or influenza disease among vaccinated patients for the most serious outcomes of IMV or death.”
Background information in the study suggested that RSV is increasingly recognized as an important cause of severe respiratory disease in adults, with an estimated 60,000 to 160,000 RSV-associated hospitalizations and 6,000 to 10,000 deaths occurring each year among adults aged 65 years and older in the United States.
The researchers noted that disease severity from an infection can be affected by host immunity, pathogen virulence, as well as by the use of therapeutics targeting either the host response or the pathogen. “Vaccination strengthens host immunity against infection and its sequelae and has been shown to attenuate both COVID-19 and influenza disease severity,” the researchers explained. “Because vaccines against COVID-19 and influenza are routinely used by adults in the U.S., a comparison of disease severity caused by RSV with that of COVID-19 or influenza, by vaccination status, could be useful for framing the potential benefits of RSV vaccination, which may include reduction in disease severity, as observed with COVID-19 and influenza vaccination.”
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