Excess Respiratory Hospitalisations Associated with Influenza, Respiratory Syncytial Virus and SARS-CoV-2 in Singapore from 2015 to 2023

Background

The patterns of circulation and burden of influenza and respiratory syncytial virus (RSV) in Singapore are affected by the COVID-19 pandemic containment measures. These patterns in relation to SARS-CoV-2 in a post-pandemic era are unclear.

Methods

Using data from 2015 to 2023, we estimated excess influenza-, RSV- and SARS-CoV-2-associated hospitalisation in Singapore, adjusted for rhinovirus/enterovirus activity in generalised additive models. The data include pneumonia and influenza (P&I) hospitalisation from a national inpatient database and a community-wide acute respiratory infection (ARI) sentinel surveillance programme, stratified by age groups.

Results

Across all age groups, the proportion of hospitalisation associated with influenza, SARS-CoV-2 and RSV was 13.2% (95% CI 5.0%–21.6%), 19.3% (95% CI 13.8%–25.0%) and 4.0% (95% CI 0.9%–12.1%) in 2023, respectively. From 2019 to 2023, all-age influenza-associated hospitalisation declined from 264.4 per 100,000 person-years (95% CI 214.2–313.2) to 203.7 per 100,000 person-years (95% CI 76.8–333.6). In contrast, all-age RSV-associated hospitalisation after the pandemic was 62.2 per 100,000 person-years (95% CI 13.8–186.9), similar to pre-pandemic observations. Peak seasonal influenza occurred 3–8 weeks later as compared with the time of pre-pandemic peak influenza activity.

Conclusion

The overall burden of influenza has declined after the COVID-19 pandemic and its burden is comparable with SARS-CoV-2. Furthermore, shifts in the timing of peak influenza activity suggest a potential need to review the timing of vaccine recommendations in Singapore.