The prevalence, incidence and longevity of antibodies against SARS-CoV-2 among primary healthcare providers in Belgium: a prospective cohort study with 12 months of follow-up
Authors: Adriaenssens Niels , Scholtes Beatrice , Bruyndonckx Robin , Van Ngoc Pauline , Verbakel Jan Y , De Sutter An , Heytens Stefan , Van den Bruel Ann , Desombere Isabelle , Van Damme Pierre , Goossens Herman , Buret Laëtitia , Duysburgh Els , Coenen Samuel 
Published: June 2022

Objectives

To estimate the prevalence, incidence, and longevity of antibodies against SARS-CoV-2 among primary healthcare providers (PHCPs).

Design

Prospective cohort study with 12 months of follow-up.

Setting

Primary care in Belgium

Participants

Any general practitioner (GP) working in primary care in Belgium and any other PHCP from the same GP practice who physically manages (examines, tests, treats) patients were eligible. A convenience sample of 3,648 eligible PHCPs from 2,001 GP practices registered for this study (3,044 and 604 to start in December 2020 and January 2021, respectively). 3,390 PHCPs (92,9%) participated in their first testing timepoint (2,820 and 565, respectively) and 2,557 PHCPs (70,1%) in the last testing timepoint (December 2021).

Interventions

Participants were asked to perform a rapid serological test (RST) targeting IgM and IgG against the receptor binding domain (RBD) of SARS-CoV-2 and to complete an online questionnaire at each of maximum 8 testing timepoints.

Primary and secondary outcome measures

The prevalence, incidence, and longevity of antibodies against SARS-CoV-2 both after natural infection and after vaccination.

Results

Among all participants, 67% were women and 77% GPs. Median age was 43 years. The seroprevalence in December 2020 (before vaccination availability) was 15.1% (95% CI: 13.5% to 16.6%), increased to 84.2% (95% CI: 82.9% to 85.5%) in March 2021 (after vaccination availability) and reached 93.9% (95% CI: 92.9% to 94.9%) in December 2021 (during booster vaccination availability and fourth (delta variant dominant) covid wave). Among not (yet) vaccinated participants the first monthly incidence of antibodies against SARS-CoV-2 was estimated to be 2.91% (95% CI: 1.80% to 4.01%). The longevity of antibodies is higher in PHCPs with self-reported COVID-19 infection.

Conclusions

This study confirms that occupational health measures provided sufficient protection when managing patients. High uptake of vaccination resulted in high seroprevalence of SARS-CoV-2 antibodies in PHCPs in Belgium. Longevity of antibodies was supported by booster vaccination and virus circulation.

Registration

Trial registration number: NCT04779424

Strengths and limitations of this study

This large cohort study with 12 months follow-up could provide precise estimates of the prevalence and incidence of antibodies against SARS-CoV-2 among primary health care providers (PHCPs) at national and regional level in Belgium.

The rapid serological test (RST) used targets IgM and IgG against the receptor binding domain of SARS-CoV-2 and could therefore also assess the antibody response after vaccination, and longevity of antibodies against SARS-CoV-2 both after natural infection and after vaccination, but cannot distinguish between both.

The results in PHCPs could be compared to that of the general population and other population groups, e.g. health care workers in hospitals and nursing homes.

The use of a convenience sample, missing data points and reduced RST accuracy when performed and interpreted by many different participants could limit the validity of the study results.