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RSV Vaccine Proves 75% Effective Against Hospitalization in Older Adults, According to New CDC Data
The new data amend that from prelicensure trials, which did not include fair representation of older adults and others more vulnerable to severe RSV disease.
Vaccination against respiratory syncytial virus (RSV) among adults aged 60 years and older was associated with 75% efficacy against RSV-related hospitalization during the first season following vaccine approval, according to new data from researchers at the CDC and Vanderbilt University.1
The team found no difference in vaccine efficacy (VE) after balancing potential confounding variables between vaccinated and unvaccinated participants (79%) or among subgroups according to age, ie, adults aged 60 to 74 years (75%) or 75 years and older.1
In their research letter published online September 4 in JAMA, investigators emphasized that prelicensure clinical trials, while demonstrating the vaccines’ high efficacy against RSV-associated lower respiratory tract disease (LRTD), left significant gaps in knowledge about their broader impact. They noted the studies were not originally powered to assess efficacy against hospitalization for the infection. Importantly, the trials did not include immunocompromised participants and underrepresented other populations at risk for severe disease and poor outcomes, including adults aged 75 and older.1 In fact, the researchers cite CDC estimates that between 60 000 and 160 000 RSV-associated hospitalizations annually are among adults who are 65 or older.2
The study authors, representing the Investigating Respiratory Viruses in the Acutely Ill (IVY) Network, designed the current research, a test-negative, case-control analysis, to evaluate VE against hospitalization for RSV in older adults and to accrue data on this population that “more closely represents those at high-risk of severe [RSV] disease.”1
The joint CDC-Vanderbilt team tapped electronic medical records for 2978 adults aged 60 years and older who were hospitalized with an acute respiratory illness at 1 of 24 sites in 19 states participating in a surveillance network between October 1, 2023, and March 31, 2024, according to the study.1 All participants were tested for RSV, SARS-CoV-2, and influenza viruses. The final cohort of case participants tested positive for RSV alone; control participants tested negative for all 3 viruses of interest.
Participants provided additional demographic information through interviews; RSV vaccination status was defined as receipt of the shot 14 days or more before a participant became ill. Researchers adjusted logistic regression models for covariates that included age, sex, race and ethnicity, region and calendar month and stratified analyses by 2 age groups, 60-74 years, and 75 years and older, according to the study. In a secondary analysis, they used inverse probability of vaccination weighting to balance potential confounders.1
FINDINGS
Of the original 2978-participant cohort, 367 (12.3%) were designated RSV cases and 2611 (87.7%) as controls, ie, did not have RSV, SARS-CoV-2, or influenza. The group had a median age of 72 years and median Charlson Comorbidity Index score was high (5). Nearly one-quarter (24.2%, 720) were identified as having immunocompromising conditions.
Among participants with RSV, 2.5% had been vaccinated against the virus compared with 9.8% of the control group, at a median 84 days before symptoms of respiratory illness, according to the study.
Participants who had received the RSV vaccine were more likely to be 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), have 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).
As above, the IVY team reported VE against RSV-associated hospitalization of 75% (95% CI, 50%-87%), efficacy that did not change after estimation using 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%).
The investigators point to several limitations that could affect generalizing beyond the study population including low uptake of the RSV vaccine in the first season it was available as well as disparities in uptake. They also considered the potential confounding effects of unmeasured variables.
Nonetheless the researchers emphasize the value of the addition their findings make to prelicensure data, providing real-world evidence of the protection vaccination offers against costly inpatient management of RSV as well as RSV VE in vulnerable populations not well studied prior to FDA approval of the shots.
"Evaluation of RSV VE in future seasons is important to confirm these findings and further examine VE among subgroups and by time since vaccination," they concluded.
The CDC first recommended in June 2023 that all adults aged 60 and older receive the RSV vaccine based on the formulations’ strong performance against infection during late-phase clinical trials. One year later,3 that guidance was changed, and the CDC’s Advisory Committee on Immunization Practices endorsed a universal recommendation for a single lifetime dose of RSV vaccine for adults 75 years and older and a risk-based recommendation for those aged 60 to 74 years.3
There are now 3 FDA-approved RSV vaccines approved for older adults. Abrysvo (Pfizer), and Arexvy (GSK) were approved in 2023. mRESVIA (Moderna), the first RSV vaccine produced using mRNA technology, was approved at the end of May 2024.
