ABSTRACT
During early 2021, Peru had the highest COVID-19-associated per-capita mortality rate globally. Socioeconomic inequality and insufficiently prepared healthcare and surveillance systems likely contributed to high mortality, potentially coupled with early SARS-CoV-2 introduction. We tested 1,441 individuals with fever sampled during August 2019-May 2021 in Lima, Peru, for SARS-CoV-2-specific antibodies. Serologic testing included a chemiluminescence immunoassay and confirmatory surrogate virus neutralization testing. Early positive samples (n=24) from January-March 2020 were further tested using a plaque-reduction neutralization and avidity tests based on SARS-CoV-2 spike and nucleoprotein antigens. None of the early samples were PRNT-confirmed, in contrast to 81.8% (18/22) of a subsample from April 2020 onwards (Fischer-exact test, p<0.0001). SARS-CoV-2 antibody detection rate was 0.9% in mid-April 2020 (1/104; 95% confidence interval (CI), 0.1-5.8%), suggesting onset of viral circulation in early-mid March 2020, consistent with the first molecular detection of SARS-CoV-2 in Peru on March 6th. Mean avidity increase of 62-77% to 81-94% from all PRNT-confirmed samples during early 2020, were consistent with onset of SARS-CoV-2 circulation during late February/March 2020. Early circulation of SARS-CoV-2 was confirmed in a Susceptible, Exposed, Infected and Recovered mathematical model that projected an effective reproduction number >1, during February-March 2020. Robust serologic testing thus confirmed that early SARS-CoV-2 introduction contributed to high COVID-19 mortality in Peru. Emphasizing the role of diagnostic confirmation, our study highlights the importance of early detection and accurate testing in managing infectious disease outbreaks.