Comparable exposure to SARS-CoV-2 in young children and healthcare workers in Zambia

Background: Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an ongoing global health crisis that has caused large scale morbidity and mortality. We aimed to determine the exposure to SARS-CoV-2 among young children and healthcare workers by measurement of anti-S1 antigen (spike protein) specific immunoglobulin G (IgG) using an in-house optimized indirect enzyme-linked immunosorbent assay (ELISA) method. Methods: Plasma samples were collected from cohorts of healthcare workers (n = 287) and young children aged from 6 weeks to 2 years old (n = 150) pre-COVID-19 pandemic between September 2018 and November 2019 and post-COVID-19 pandemic between August and December 2020 were simultaneously tested for anti-SARS-CoV-2 S1 specific IgG. The arithmetic mean of natural logarithm-transformed ELISA relative absorbance reading + (3 x standard deviation) of pre-pandemic plasma was used as the cut-off to determine SARS-CoV-2 IgG seropositivity of post-pandemic plasma. Results: There was no reactivity to SARS-CoV-2 S1 antigen detected in pre-pandemic plasma but in post pandemic plasma an 8.0% (23/287) IgG seropositivity in healthcare workers’ and 6.0% (9/150) seropositivity in children aged 2 years old was detected. Conclusions: Comparable levels of SARS-CoV-2 IgG seropositivity in healthcare workers and children suggest widespread exposure to SARS-CoV-2 in Zambia during the first wave of the pandemic. This finding has implications for continued acquisition and transmission of infection in the healthcare setting, household, and wider community.