# Seroprevalence of SARS-CoV-2 nucleocapsid antibody among sex workers during the 5th epidemic wave with Omicron variant in Chiang Mai, Thailand

## TL;DR

This study found a 42.4% rate of SARS-CoV-2 antibodies in sex workers in Chiang Mai, Thailand, with higher rates among non-Thai individuals and those with a history of COVID-19.

## Contribution

The study provides new insights into SARS-CoV-2 seroprevalence among sex workers during the Omicron wave in Thailand.

## Key findings

- Seroprevalence of SARS-CoV-2 NC-Ab IgG was 42.4% among sex workers in Chiang Mai.
- Non-Thai sex workers had significantly higher seroprevalence than Thai sex workers.
- Vaccination status did not affect NC-Ab seroprevalence.

## Abstract

To investigate the seroprevalence of SARS-CoV-2 nucleocapsid antibodies (NC-Ab) in sex workers.

A cross-sectional/observational study was conducted between March and December 2022 among sex workers living in Chiangmai, Thailand, aged over 18 years and who had engaged in sex work in the previous 12 months. Consenting individuals completed a questionnaire and had blood drawn. IgG-specific for SARS-CoV-2 nucleocapsid was assessed using Euroimmun anti-SARS-CoV-2 NCP ELISA (IgG).

264 sex workers (52.3 % male) with a median age 31 years were included. The overall seroprevalence of SARS-CoV-2 NC-Ab was 42.4 % (44.2 % in males, 40.5 % in females). It was significantly higher among non-Thai than Thai sex workers (57.1 % vs. 37.1 %, p = 0.004) and among individuals who reported a history of COVID-19 as compared those who did not (54.9 % vs. 34.3 %, p = 0.036). NC-Ab seroprevalence did not differ by sex, age, receipt of COVID-19 vaccines, or the number of vaccine doses. SARS-CoV-2 NC-Ab seropositivity was significantly associated with being non-Thai, having monthly income >15,000 Baht, having received inactivated COVID-19 vaccines, and having been diagnosed with COVID-19.

This study shows a high seroprevalence of NC-Ab among sex workers in Chiangmai, Thailand during the fifth epidemic wave with Omicron variant. This may be due to combined effects of high transmissibility of the Omicron variant and high-risk behavior of those individuals. Specific health education interventions are needed for this specific population.

•Seroprevalence of SARS-CoV-2 NC-Ab IgG was 42.4 % among sex workers in Chiangmai, Thailand.•NC-Ab IgG seroprevalence was significantly higher among non-Thai than Thai.•NC-Ab IgG seroprevalence was high among sex workers who reported an history of COVID-19.•No difference of NC-Ab seroprevalence between unvaccinated and vaccinated sex workers.

Seroprevalence of SARS-CoV-2 NC-Ab IgG was 42.4 % among sex workers in Chiangmai, Thailand.

NC-Ab IgG seroprevalence was significantly higher among non-Thai than Thai.

NC-Ab IgG seroprevalence was high among sex workers who reported an history of COVID-19.

No difference of NC-Ab seroprevalence between unvaccinated and vaccinated sex workers.