This is a summary, written by members of the CITF Secretariat, of:

Bergeri I, Whelan M, Ware H, Subissi L, Nardone A, Lewis HC, Li Z, Ma X, Valenciano M, Cheng B, Al Ariqi L, Rashidian A, Okeibunor J, Azim T, Wijesinghe Le LV, Vaughan A, Pebody R, Vicari A, Yan T, Yanes-Lane M, Cao C, Cheng MP, Papenburg J, Buckeridge D, Bobrovitz N, Arora RK, van Kerkhove MD, Unity Studies Collaborator. Global epidemiology of SARS-CoV-2 infection: a systematic review and meta-analysis of standardized population-based seroprevalence studies, Jan 2020-Dec 2021.  medRxiv 2022 Feb 14 doi: 10.1101/2021.12.14.21267791v2

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A study carried out by SeroTracker (a CITF-funded project), in partnership with the World Health Organization, found global SARS-CoV-2 seroprevalence (due to infection or vaccination or both) was 45.2% by end of June 2021. Depending on the region, seroprevalence varied from as low as 2.5% to as high as 94.9%. In the second quarter of 2021, the ratio of seropositive blood samples to identified cases in low and middle-income countries was approximately 45.3:1, suggesting that many infections were still going undetected in a period where vaccines were not yet widely available. The study is a preprint, which has been updated, and not yet been peer reviewed.

Key findings:

  • Combined seroprevalence from infection or vaccination globally was 45.2%; global seroprevalence excluding vaccination was 35.2%, which was a considerable increase from 5.5% in June 2020.
  • The median ratio of combined seroprevalence to identified cases, globally, was 17:1 in April-June 2021. By region, in April- June 2021, this ranged from 1.2:1 in Europe to 183:1 in Africa.
  • The median asymptomatic combined seroprevalence was similar between males and females (61.1% vs 55.7%).

A total of 50% of WHO member states (97/194) and four countries, areas and territories, across all six WHO regions, were represented in this study.

To determine the global seroprevalence of SARS-CoV-2, a systematic review and meta-analysis was conducted. A total of 431 full texts, comprising 803 unique studies carried out from January 1, 2020 to December 30, 2021, were included in the analysis for this manuscript. This included published studies, pre-prints, and results from WHO UNITY study collaborators who had not yet made results available to the general public.

These findings provide a detailed picture of global seroprevalence, demonstrating stark differences between regions, as well as an in-depth breakdown by age group. Seroprevalence data that is of high quality and standardized (such as the WHO UNITY studies) continue to be essential to inform health policy decision-making around COVID-19 control measures, particularly in resource limited regions with low vaccination rates.

See a summary of earlier data reported by this research team, covering January 2020 to October 2021, here.

Explore the SeroTracker dashboard here.