What was the global SARS-CoV-2 seroprevalence from January 2020 to April 2022?

By Bhavana KunkalikarReviewed by Aimee MolineuxNov 14 2022

In a recent study published in PLoS Medicine, researchers assessed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence worldwide between January 2020 and April 2022.

Since the beginning of the coronavirus disease 2019 (COVID-19) pandemic in 2020, research is still lacking in understanding SARS-CoV-2. Routine surveillance statistics underestimate the extent and number of infections and hence cannot be used to infer community immunity, especially since there is a preponderance of asymptomatic infections and disparate access to diagnostic tests.

Since anti-SARS-CoV-2 antibodies are important markers of immune protection, studies related to seroprevalence indicate humoral immunity elicited at population levels. This, in turn, is essential for informing scenario modeling, public health planning, and national policies to curb the pandemic.

About the study

In the present study, researchers determined the level of population infection and seropositivity by meta-analyzing SARS-CoV-2 seroprevalence data for the general population.

The team performed a systematic evaluation of seroprevalence studies published between 1 January 2020 and 20 May 2022, which was reported per the Preferred Reporting Items Systematic Review and Meta-Analyses (PRISMA) standards. Secondary research and the article capture method involved contributions to the study database via the open-access SeroTracker platform and suggestions from international experts, as well as material collated through the World Health Organization (WHO) Unity research project.

The screening of studies, data extraction, and critical evaluation was performed in duplicate by a team of 13 research authors. Inclusion and exclusion criteria corresponded with the standard seroepidemiological investigation (SEROPREV) protocol to minimize potential bias induced by interstudy variability and other indicators of study quality, including poor assay performance and/or sampling techniques. Cross-sectional and longitudinal cohort studies were considered to estimate the seroprevalence of SARS-CoV-2 in the general population.

Inclusion criteria included home-based and community samples, as well as studies where a strong sampling frame was specified that approximated a larger population. In addition, the study cohort included people living in slum homes and patient groups in humanitarian circumstances. Using established formulae for parallel and serial testing, multi-assay testing algorithms were implemented if the aggregate specificity and sensitivity matched the performance criteria. Two members of the study team assessed complex multiple-testing strategies involving three or more tests on a case-by-case basis.

Per the protocol, seroprevalence estimates were derived from each trial and stratified as per age, gender, vaccination status, and time of specimen collection. Data regarding the study population, the laboratory assay employed, and any adjustments made to the seroprevalence estimate were extracted.

Results

The team identified 173,430 titles and abstracts between 1 January 2020 and 20 May 2022. Among these, 5,281 full-text articles were part of the full-text screening process. Approximately 513 seroprevalence data sources comprising research performed following the SEROPREV methodology were identified, 480 published, and collaborators compiled 33. The 513 seroprevalence sources included 965 distinct seroprevalence studies. The study included 52% of WHO Member States (MS) and four WHO nations, areas, and territories represented in the seroprevalence studies.

In a series of meta-analyses, the team computed weighted seroprevalence and found that in September 2021, the global seroprevalence induced by vaccination or infection was 59.2%, which was a 7.7% increase from the June 2020 estimate. In September 2021, the global infection-attributable seroprevalence was 35.9%.

In February 2021, the overall seroprevalence in the Eastern Mediterranean region (EMR) was 42.7%, while the same in June 2020 was 33.6%. In April 2021, the overall seroprevalence in the Americas region (AMR) low- and middle-income country (LMIC) was 20% which was 2.3-fold that in June 2020. In June 2021, the overall seroprevalence in the Europe region (EUR) LMIC was 48.7%, up from the 22.4% noted in July 2020. As of September 2021, the South-East Asia region (SEAR) had an overall seroprevalence of 82.2%, which was 8.9-fold more than that in June 2020.  Total seroprevalence in December 2021 for the Africa region (AFR) was 86.7%, compared to 3.5% in June 2020, which in the Western Pacific region (WPR) was 30.3%, compared to 0.2% in June 2020. In March 2022, the total seroprevalence in EUR high-income country (HIC) was 95.9%, compared to 4.3% in June 2020, which was 99.8% in AMR (HIC), compared to 3.6% in June 2020. In March 2022, 47.9% of the EUR HIC population and 33.7% of the AMR HIC population had infection-induced antibodies.

Conclusion

The study findings showed that the global seroprevalence had increased significantly over time and with geographical heterogeneity. Yet, more than one-third of the global population was SARS-CoV-2-seronegative. infections estimated by the study based on seroprevalence greatly surpass the documented cases of COVID-19. Seroprevalence investigations of high quality and standard are critical for informing the COVID-19 response, especially in countries with limited resources.