Hybrid, vaccine-induced and natural immunity against SARS-CoV-2 in traditional food markets in Bolivia (2020−2022): A cross-sectional analysis of a serological survey

Background

In low-and middle-income countries, market vendors played a crucial role in food security during the coronavirus pandemic. High numbers of contacts, combined with social, political and health system upheaval in Bolivia, meant they were highly exposed to SARS-CoV-2 infections.

Methods

Demographic, clinical and serological data were collected at survey rounds between 2020 and 2022 from a cohort of market vendors in two purposively selected markets where the community and researchers co-promoted health and safety. We used these longitudinal data to examine SARS-CoV-2 anti-spike antibody levels between those vaccinated with and without previous infection and those unvaccinated. The association between antibody levels, and vaccine status, socio-demographic and health information was assessed using linear regression.

Findings

A total of 213 market vendors had repeated serological sampling in July, and November 2021, and again in May 2022. In November 2020, 105 (49.3 %) of this cohort had participated in a pre-vaccination municipal serological survey. Seroprevalence then was 45·7 % (95 %CI 36·3–55·4). By November 2021, 67·8 % of the full cohort had one vaccination and seroprevalence was 83·6 %. We showed IgG levels in those seropositive were higher in participants with evidence of vaccination and prior infection compared to those unvaccinated. By May 2022, the majority of participants developed antibodies against SARS-CoV-2, and these differences were attenuated.

Interpretation

A substantial proportion of vendors were susceptible to SARS-CoV-2 in late 2020 when, nationally, excess mortality was high. Our analyses suggested a combination of natural infection and vaccination provided better protective antibody levels than natural infection alone at the peak of the pandemic. Future pandemic planning requires timely targeted serological surveys to understand pandemic dynamics and support prompt interventions. In addition, communication with organized communities can inform effectiveness of pandemic mitigation strategies including improved vaccination uptake. Timely quantitative IgG level monitoring can also inform waning immunity.

Funding

This study was supported by the Medical Research Council and a National Institutes for Health and Care Research (NIHR) Global Effort on COVID-19 (GECO) Health Research award 2020 [MR/V028561/1].