Echeverria G, Guevara A, Coloma J, Ruiz AM, et al. Pre-existing T-cell immunity to SARS-CoV-2 in unexposed healthy controls in
Ecuador, as detected with a COVID-19 Interferon-Gamma Release Assay. Int J Infect Dis 2021 Feb 11. pii: S1201-9712(21)00120.
PMID: 33582369