Antibody Response in Healthcare Workers During the Severe Acute Respiratory Syndrome Coronavirus 2 Gamma Variant Outbreak in Manaus, Brazil.

Publication date: Jul 16, 2025

This study aimed to evaluate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific binding and neutralizing antibody responses in healthcare workers (HCWs) who received coronavirus disease 2019 (COVID-19) vaccines, with or without postvaccination infections. We conducted a prospective, observational cohort study of HCW in 2 hospitals in Manaus, Brazil. From 31 March through 31 May 2021, HCWs had nasal swabs collected and questionnaires administered weekly for 4 visits. Nasal swabs were tested for SARS-CoV-2 by real-time reverse transcription polymerase chain reaction (rRT-PCR). Blood specimens were obtained at visits 1 and 4 unless the HCW was found to be infected. If infected, a blood specimen was collected on days 14 and 28 after symptom onset or date of positive specimen, if asymptomatic. COVID-19 vaccination cards, state immunization records, and self-reported history of previous SARS-CoV-2 infection were obtained. Fully vaccinated HCWs who tested SARS-CoV-2 rRT-PCR positive were classified as postvaccination infections. A total of 771 HCWs were enrolled, with 73. 7% (568/771) fully vaccinated. Anti-SARS-CoV-2 S1 immunoglobulin G and neutralizing antibody levels showed steep decay within the first 50 days after COVID-19 vaccination. HCWs with prior SARS-CoV-2 infection had slower visible decay after 50 days compared with those without prior infection. We identified 12 postvaccination infections of 16 HCWs who were SARS-CoV-2 rRT-PCR+, including 4 who also reported previous infection. Those positive for SARS-CoV-2 had lower baseline neutralizing antibody levels against Gamma and Delta variants preinfection (median log10 titers [interquartile range]: Gamma, 1. 5 [3]; Delta: 0 [0. 25]) compared to those who remained rRT-PCR negative (median log10 titers [interquartile range]: Gamma, 3 [2]; Delta, 1 [2]). Our findings highlight the importance of routine antibody surveillance, targeted boosters, and hybrid immunity in low and middle income countries. Timely booster doses for HCWs and the development of new vaccines against emerging variants can help sustain immunity and prevent workforce shortages, strengthening healthcare resilience in resource-limited settings.

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