The impact of COVID-19 pandemic on influenza surveillance: a systematic review and meta-analysis

Background

Influenza activity was reported to be below the seasonal levels during the COVID-19 pandemic globally. However, during the SARS-CoV-2 outbreak, the routine real-time surveillance of influenza like illness (ILI) and acute respiratory infection (ARI) was adversely affected due to the changes in priorities, economic constraints, repurposing of hospitals for COVID care and closure of outpatient services.

Methods

A systematic review and meta-analysis were carried out to assess the pooled proportion of symptomatic cases tested for influenza virus before the current pandemic in 2019 and during the pandemic in 2020/21. An electronic search of PubMed/MEDLINE, Scopus and Google Scholar was carried out for the articles reporting the impact of the COVID-19 pandemic on Influenza surveillance among humans using search terms. The study was designed based on PRISMA guidelines and the meta-analysis was performed to synthesise the pooled proportion of patients sampled for influenza with 95% confidence interval (CI).

Results

The nine qualified studies from the WHO-European region, Canada, Japan, Germany, Italy, Spain, South Africa and the United States were pooled by random-effects meta-analysis. The overall pooled proportion of symptomatic cases sampled for influenza surveillance before and during the pandemic was 2.38% (95% CI 2.08%-2.67%) and 4.18% (95% CI 3.8%-4.52%) respectively. However, the pooled proportion of samples tested for influenza before the pandemic was 0.69% (95% CI 0.45-0.92%) and during the pandemic was 0.48% (95% CI 0.28-0.68%) when studies from Canada were excluded.

Conclusion

The meta-analysis concludes that globally there was a decline in influenza surveillance during the COVID-19 pandemic except in Canada.

Key Messages

• The nine observational studies from Europe, Canada, Japan, South Africa and the United States were qualified for the meta-analysis

• A steep decline in the seasonal influenza activity in both northern and southern hemispheres was observed

• Almost double the number of symptomatic cases were sampled as part of influenza surveillance during the current pandemic in Canada

• Except in Canada, a decline in influenza surveillance globally during the COVID-19 pandemic was observed