# A cross-sectional study of SARS-CoV-2 antibodies among healthcare workers in a tertiary care hospital in Taiwan: implications for protection against the Omicron variants

## TL;DR

This study examines antibody responses in healthcare workers in Taiwan to determine protection against Omicron variants following vaccination and prior infection.

## Contribution

The study provides new insights into the effectiveness of vaccination and natural immunity against Omicron subvariants in healthcare workers.

## Key findings

- 20.2% of healthcare workers achieved seroprotection against Omicron subvariants BA.1, BA.4, and BA.5.
- Anti-Spike S1 protein IgG levels showed a decay curve below 20,000 AU/ml after 120 days.
- The optimum Anti-S was 41,328 AU/mL with 86.1% sensitivity and 63.5% specificity.

## Abstract

Taiwan, deeply impacted by the 2003 SARS outbreak, promptly implemented rigorous infection control and prevention (ICP) measures in January 2020 to combat the global COVID-19 pandemic. This cross-sectional serologic study was conducted among healthcare workers (HCWs) in a tertiary care hospital in Taiwan from August 1, 2022, to February 28, 2023. The study aimed to assess HCWs’ antibody responses to COVID-19 vaccination against Omicron subvariants BA.1, BA.4, and BA.5, considering variations in prior infection. Additionally, it evaluated the effectiveness of ICP and vaccination policies within the hospital setting in Taiwan.

A cross-sectional serology study was conducted in Taiwan to investigate the seroprevalence rates of Omicron subvariants BA.1, BA.4, and BA.5 among HCWs. A total of 777 HCWs participated in this study. A structured questionnaire was collected to obtain the epidemiological characteristics and risk factors for potential exposure. Enzyme-linked immunosorbent assay was used to detect antibody responses. Serum samples were selected for protection against Omicron subvariants BA.1, BA.4, and BA.5 by using a pseudotyped-based neutralization assay.

More than 99% of the participants had received SARS-CoV-2 vaccination. Overall, 57.7% had been infected with SARS-CoV-2, with some being asymptomatic. The SARS-CoV-2 Anti-Spike S1 protein IgG (Anti-S) distribution was 40,000 AU/mL for 20.2% (157/777) of participants, with a mean ± standard deviation of 23,442 ± 22,086. The decay curve for Anti-S was less than 20,000 AU/ml after 120 days. The probability curve of 50% neutralization showed an Anti-S of 55,000 AU/ml. The optimum Anti-S was 41,328 AU/mL (equal to 5,869 WHO’s standard BAU/mL), with 86.1% sensitivity and 63.5% specificity.

In this significant study, 20.2% of HCWs achieved seroprotection against Omicron subvariants BA.1, BA.4, and BA.5. Their immunity against Omicron subvariants was further reinforced through recommended vaccinations and the development of natural immunity from SARS-CoV-2 exposure, collectively enhancing their protection against Omicron.

The online version contains supplementary material available at 10.1186/s12879-024-09411-z.