Systematic review of seroprevalence of SARS-CoV-2 antibodies and appraisal of evidence, prior to the widespread introduction of vaccine programmes in the WHO European Region, January-December 2020

Abstract

Objectives: Systematic review of SARS-CoV-2 seroprevalence studies undertaken in the WHO European Region to measure pre-existing and cumulative seropositivity prior to the roll out of vaccination programmes.

Design: A systematic review of the literature.

Data sources: We searched MEDLINE, EMBASE and the preprint servers MedRxiv and BioRxiv in the WHO 'COVID-19 Global literature on coronavirus disease' database using a predefined search strategy. Articles were supplemented with unpublished WHO-supported Unity-aligned seroprevalence studies and other studies reported directly to WHO Regional Office for Europe and European Centre for Disease Prevention and Control.

Eligibility criteria: Studies published before the widespread implementation of COVID-19 vaccination programmes in January 2021 among the general population and blood donors, at national and regional levels.

Data extraction and synthesis: At least two independent researchers extracted the eligible studies; a third researcher resolved any disagreements. Study risk of bias was assessed using a quality scoring system based on sample size, sampling and testing methodologies.

Results: In total, 111 studies from 26 countries published or conducted between 1 January 2020 and 31 December 2020 across the WHO European Region were included. A significant heterogeneity in implementation was noted across the studies, with a paucity of studies from the east of the Region. Sixty-four (58%) studies were assessed to be of medium to high risk of bias. Overall, SARS-CoV-2 seropositivity prior to widespread community circulation was very low. National seroprevalence estimates after circulation started ranged from 0% to 51.3% (median 2.2% (IQR 0.7-5.2%); n=124), while subnational estimates ranged from 0% to 52% (median 5.8% (IQR 2.3%-12%); n=101), with the highest estimates in areas following widespread local transmission.

Conclusions: The low levels of SARS-CoV-2 antibody in most populations prior to the start of vaccine programmes underlines the critical importance of targeted vaccination of priority groups at risk of severe disease, while maintaining reduced levels of transmission to minimise population morbidity and mortality.

Keywords: COVID-19; epidemiology; infectious diseases; public health; systematic review.

Figure 1

PRISMA flow chart of SARS-CoV-2 seroprevalence study selection. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Figure 2

Geographical distribution of SARS-CoV-2 seroprevalence studies published in the WHO European Region between 1 January2020 and 31 December 2020. Countries with national-level seroprevalence studies are reported in blue (shade of blue reflects the number of studies conducted in the country/territory). Subnational-level seroprevalence studies are reported as a yellow circle (size of circle reflects number of subnational studies conducted in the country/territory). A number of studies are listed in boxes under name. Countries with not studies are coloured in grey. The designations employed and the presentation of this material do not imply the expression of any opinion whatsoever on the part of the secretariat of the WHO concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers and boundaries. Dotted and dashed lines on maps represent approximate locations for which there may not yet be full agreement.

Figure 3

National (A) and subnational (B) seroprevalence estimates of SARS-CoV-2 antibodies over time in the WHO European Region (1 January 2020–31 December 2021).

Figure 4

Correlation between seroprevalence point estimates from low to medium risk of bias studies and cumulative (A) incidence and (B) deaths in all populations, in the WHO European Region (1 january 2020–31 December 2020).