New CDC-led research noted that prelicensure trials were not powered to assess efficacy against RSV-associated hospitalization and excluded immunocompromised patients. In addition, the trials underrepresented other groups at increased risk of severe RSV disease, including adults aged 75 years and older. In response, a study team evaluated RSV vaccine effectiveness (VE) against RSV-associated hospitalization among adults aged 60 years and older during the first season of use. The results were published as a research letter in the Journal of the American Medical Association.
The test-negative, case-control analysis included adults aged 60 years and older hospitalized with acute respiratory illness who had clinical respiratory virus testing within 10 days of illness onset at one of 24 hospitals in the 19 states participating in a surveillance network. The study ran from October 1, 2023, to March 31, 2024.
The researchers obtained nasal swabs and systematically tested them by reverse transcription polymerase chain reaction for RSV, SARS-CoV-2, and influenza viruses. For purposes of the study, case patients tested positive for RSV only and control patients tested negative for RSV, SARS-CoV-2, and influenza.
The study team obtained demographic and clinical data through patient interview and electronic medical record review, while RSV vaccination status—defined as RSV vaccine receipt 14 days or more before illness onset—was determined from electronic medical records, immunization registries, and self-reports.
Of the 2,978 adult participants aged 60 years and older, 367 (12.3%) were RSV case patients and 2,611 (87.7%) were control patients. They had a median (interquartile range [IQR]) age of 72 (66-80) years, median (IQR) Charlson Comorbidity Index score of 5 (4-7), and 24.2% were immunocompromised.
Of the 288 RSV case patients with known RSV subtype, 210 (72.9%) were RSV B. Only nine of 367 (2.5%) case patients and 256 of 2,611 (9.8%) control patients were vaccinated, with a median (IQR) interval between vaccination and illness onset of 84 (54-125) days.
Compared with unvaccinated patients, the researchers pointed out that vaccinated patients were more frequently older (median age, 75 vs. 72 years; P <.001); white (82.6% vs. 60.7%; P <.001); immunocompromised (31.7% vs. 23.4%; P <.01); had outpatient visits in the past year (95.9% vs. 90.1%; P <.01); and resided in communities with a lower Social Vulnerability Index score (median, 0.37 vs. 0.58; P <.001).
The results indicated VE against RSV-associated hospitalization was 75% (95% CI, 50%-87%) and did not differ when estimated with inverse probability of vaccination weighting (79%; 95% CI, 56%-90%) or among adults aged 60 to 74 years (75%; 95% CI, 31%-91%) or 75 years and older (76%; 95% CI, 40%-91%).
“Among adults aged 60 years and older in 19 U.S. states, RSV vaccination was associated with a reduced likelihood of hospitalization with RSV compared with no vaccination,” the authors advised. “These findings expand upon prelicensure trial results in 2 ways. First, they provide evidence of vaccine protection against RSV-associated hospitalization, of which an estimated 60,000 to 160,000 occur annually among US adults aged 65 years and older. Second, they demonstrate protection in a population that more closely represents those at high risk of severe RSV disease, including adults aged 75 years and older and those with immunocompromising conditions.”
The study was limited because of disparities in RSV vaccine uptake and low uptake in the first season of use, the researchers wrote, adding, “Evaluation of RSV VE in future seasons is important to confirm these findings and further examine VE among subgroups and by time since vaccination.”
In June 2024, the CDC updated its RSV vaccination guidance for older adults, recommending that all adults aged 75 years and older and those aged 60 to 74 years at increased risk for severe RSV disease receive a single dose of RSV vaccine.
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