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In the years before the introduction of respiratory syncytial virus (RSV) vaccines, the virus was linked with substantial hospitalizations, intensive care unit (ICU) admissions, and in-hospital deaths among adults, according to a cross-sectional analysis of CDC data.

Adjusted analysis showed estimated RSV-associated hospitalization rates ranging from 48.9 per 100,000 adults during the 2016-2017 respiratory season to 76.2 per 100,000 in 2017-2018, reported researchers led by Fiona Havers, MD, MHS, of CDC's National Center for Immunizations and Respiratory Diseases in Atlanta.

Estimated hospitalization rates were highest among adults ages 75 and older, ranging from 244.7 per 100,000 in 2022-2023 to 411.4 per 100,000 in 2017-2018, findings in indicated.

In addition, annual estimates of RSV-associated ICU admissions ranged from 24,400 to 34,900 for the 2016-2017 and 2017-2018 seasons, respectively, while estimated annual in-hospital deaths ranged from 4,680 in 2018-2019 to 8,620 in 2017-2018.

"These findings validated RSV as a substantial contributor to respiratory illness and hospitalization among adults, especially older adults," Havers and colleagues wrote, noting that up to 136,000 estimated annual hospitalizations occurred among those 65 years or older.

Researchers used data from the CDC's RSV Hospitalization Surveillance Network ( to arrive at their estimates. From the database, they identified a total of 16,575 laboratory-confirmed RSV-associated hospitalizations from the 2016-2017 to the 2022-2023 respiratory virus seasons. To estimate RSV burden, Havers and colleagues used adjustment multipliers to correct for the relatively low proportion of adults who were actually tested for RSV while hospitalized, as well as test sensitivity.

Of note, RSV severity "appeared to be comparable to or possibly more than the severity of influenza and SARS-CoV-2" in hospitalized adults. In the study, about 19% of adults hospitalized with RSV required ICU care and 4.3% died in the hospital. In comparison, CDC data from the 2021-2022 season found that 15.5% of hospitalized adults with COVID-19 required ICU admission and 4.6% died, and 13.3% of patients hospitalized for the flu were admitted to the ICU and 4.6% died, they explained.

Also, estimates of RSV-associated hospitalizations in older adults were comparable to the burden of influenza-associated hospitalizations during milder influenza seasons.

Hospital deaths associated with RSV were highest among those ages 75 or older, at 5.8%. From the 2016-2017 respiratory season through the 2022-2023 seasons, adults 75 and older accounted for 45.6% of the hospitalizations, 38.6% of the ICU admissions, and 58.7% of the in-hospital deaths associated with RSV.

Deaths due to RSV were probably underestimated because the analysis did not include deaths after hospital discharge, Havers and colleagues noted.

The first-ever RSV vaccine (Arexvy) received FDA approval in May 2023, followed by approval of a second vaccine (Abrysvo) in June 2023. An mRNA RSV vaccine (mResvia) was approved earlier this year as well. CDC recommendations now say that all adults ages 75 and older should receive a single dose of an RSV vaccine, as should those ages 60 to 74 years who are at increased risk of severe RSV disease.

"Given the large numbers of potentially vaccine-preventable hospitalizations and deaths associated with RSV, increasing vaccine coverage among adults at highest risk could reduce associated hospitalizations and severe clinical outcomes," the authors wrote.

Atypical patterns of RSV circulation occurred during the COVID pandemic. Lower hospitalization rates were observed during 2020-2021 and 2021-2022, whereas increased circulation and an earlier peak occurred during 2022-2023.

On average, only 43.5% of the hospitalized adults with acute respiratory illness whose data was included in the RSV-NET catchment were tested for RSV. During 2016-2017, RSV testing was performed in 30.4% of adults ages 18-49 years with acute respiratory illness, 33.1% in those ages 50-64 years, 31.5% for those ages 65-74 years, and just 27.7% of those ages 75 and older. During the 2022-2023 season, these proportions increased to 56.1%, 61.2%, and 61.6% for those age groups, respectively.

Clinicians frequently don't test for RSV in hospitalized adults with respiratory illness because of limited awareness of RSV as an important pathogen and because results do not generally change disease management, the study authors noted. Importantly, standard tests for RSV are now recognized to have lower sensitivity than previously thought.

The analysis had several limitations, including that RSV-NET data may not be generalizable to the entire country. Also, assumptions used in the adjustment analysis may have overestimated or underestimated the burden of RSV disease.

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