Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2025 Apr;54(4):795-800.
doi: 10.18502/ijph.v54i4.18417.

A Case Study on Trends in Acute Respiratory Illnesses and Influenza in Singapore: Pre-, during, and Post-COVID-19 Pandemic

Kee Leng Chua  1 , Hwang Ching Chan  2 , Jyoti Somani  3 , See Ming Lim  4
Affiliations

A Case Study on Trends in Acute Respiratory Illnesses and Influenza in Singapore: Pre-, during, and Post-COVID-19 Pandemic

Kee Leng Chua et al. Iran J Public Health. 2025 Apr.

Abstract

Background: We investigated trends in acute respiratory illnesses and influenza activity in Singapore throughout the COVID-19 pandemic.

Methods: Publicly available data from the Ministry of Health, Singapore was used to estimate the number of daily acute respiratory illnesses (ARI) and influenza cases between 2019 and Jun 2023. Overseas travel activity was obtained from the Department of Statistics, Singapore. Trends in ARI and influenza activity during different phases of the COVID-19 pandemic with changes in key public health measures were compared.

Results: Pre-pandemic influenza activity exhibited seasonal peaks in Jan and Jul, with daily estimated cases exceeding 40 during these periods. During the early pandemic, influenza cases declined sharply to close to zero and remained at these levels until mid-2022, even after public health measures were eased. ARI cases followed a similar initial decline but gradually returned to pre-pandemic levels by 2023, with peaks occurring outside the usual seasonal pattern. These trends corresponded with phases of public health measures, including mask-wearing and travel restrictions.

Conclusion: Several hypotheses for these contrasting trends were explored, including increased public health awareness, higher influenza vaccination rates, and potential virus-virus interactions.

Keywords: Acute respiratory illness (ARI); COVID-19; Influenza; Public health measures; Viral interference.

PubMed Disclaimer

Figures

Fig. 1:
Fig. 1:
Average daily number of ARI patients seen in polyclinics per epidemiological week (Ewk) from January 2019 to June 2023
Fig. 2:
Fig. 2:
Estimated daily number of influenza cases seen in polyclinics per epidemiological week (Ewk) from January 2019 to June 2023
See this image and copyright information in PMC

References

    1. Wong S-Y, Lam M-S. (2021). Influenza Burden and its implications in 2020. The Singapore Family Physician 48–50.
    1. Bonacina F, Boëlle PY, Colizza V, Lopez O, Thomas M, Poletto C. (2023). Global patterns and drivers of influenza decline during the COVID-19 pandemic. Int J Infect Dis, 128:132–139. - PMC - PubMed
    1. Pendrey CGA, Strachan J, Peck H, et al. (2023). The re-emergence of influenza following the COVID-19 pandemic in Victoria, Australia, 2021 to 2022. Euro Surveill, 28 (37):2300118–2300118. - PMC - PubMed
    1. Centers for Disease Control and Prevention (2023). Influenza Activity in the United States during the 2022–23 Season and Composition of the 2023–24 Influenza Vaccine. https://www.cdc.gov/flu/whats-new/22-23-summary-technical-report.html
    1. European Centre for Disease Prevention and Control (2023). Seasonal influenza - Annual Epidemiological Report for 2022/2023. https://www.ecdc.europa.eu/en/publications-data/seasonal-influenza-annua...

LinkOut - more resources