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-Oct 2021.  GroupmedRxiv 2021.12.14.21267791; doi:

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) was 26% in April 2021. Depending on the region, seroprevalence varied from as low as 1.6% to as high as 57%. In low and middle-income countries, the ratio of seropositive blood samples to identified cases varied from 30:1 to 185:1, meaning that many infections were still going undetected. The study is a preprint and has therefore not yet been peer reviewed.

Key findings:

  • Combined seroprevalence from infection or vaccination globally was 26.0%; global seroprevalence excluding vaccination was 20.9%, which was a considerable increase from 8.3% in October 2020.
  • The median ratio of combined seroprevalence to identified cases, globally, was 34:1 in July-September 2020 and 16:1 in January-March 2021. By region, in January-March 2021, this ranged from 2:1 in Europe to 185:1 in Africa.
  • Median asymptomatic combined seroprevalence was similar across age groups, ranging from 54.5% in ages 50-59 to 69.4% in ages 30-39. The median asymptomatic combined seroprevalence was similar between males and females (59.8% vs 51.4%).

A total of 45% of WHO Member States (88/194) 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 396 full texts, comprising 737 unique studies carried out from January 1, 2020 to October 29, 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.