Respiratory Syncytial Virus infections in immunosuppressed adults <65 years old: a comparative analysis with Influenza and SARS-CoV2

Objectives

Respiratory Syncytial Virus (RSV) vaccine policies have varied globally since their approval in 2023. In the UK, policy has adapted in line with National evidence generation such that from Autumn 2026 at-risk persons ≥65 years old will become eligible for vaccination. Immunosuppressed persons <65 years will still not be offered protection. The objective of this study is to investigate the relative burden of RSV infection by age and immunosuppressed status (IC).

Design

Retrospective observational cohort study using routine healthcare data from North West London Integrated Care System.

Participants

Patients with a confirmed diagnosis of a respiratory viral infection (RSV, Influenza A and B, SARS-CoV2) between October 2021 and July 2025.

Main outcomes measures

Prevalence and severity of RSV infection in immunosuppressed persons <65 years old, and to provide a comparative analysis with Influenza and SARS-CoV2 in a sub-cohort tested using a 4-in-1 combined rapid PCR test.

Results

During the study period, 1226 patients were diagnosed with RSV of whom 596 (48.6%) were <65 years old. In 1091 patients with clinical data, 341 (31.3%) were IC. Fifty (9.9%) patients <65 years old had severe infection (ICU admission or death within 28 days of diagnosis), of whom 14 (28.0%) were IC. Proportionally, 16.7% of all RSV-associated deaths and 55.1% of all ICU RSV-admissions occurred in adult patients <65 years old.

RSV accounted for 665 (10.1%) infections confirmed by 4-in-1 viral PCR testing. Eight-nine (13.4%), 172 (9.3%) and 448 (12.0%) patients with RSV, Influenza A and SARS-COV2 experienced severe infection, of whom 32 (36.0%), 82 (47.7%) and 156 (34.8%) were <65 years old respectively. Eight (25.0%), 20 (24.4%) and 52 (33.3%) of patients <65 years old with severe infection were IC. On adjusted analysis, having an immunosuppressive condition increased the odds of a severe SARS-CoV2 infection, OR (95% CI) 1.36 (1.08-1.71) but not a severe RSV or Influenza infection.

Conclusions

Severe RSV infections occur in persons <65 years old, with a significant proportion of patients having an immunosuppressive condition. Urgent research is needed to investigate the potential benefit of extending the current UK RSV vaccine policy to protect younger immunosuppressed adults.