A novel application of delayed-type hipersensitivity reaction to measure cellular immune response in SARS-CoV-2 exposed individuals

•Description of a new application of an old in vivo test method.•DTH cutaneous test using a coronavirus protein to investigate immune T-cell response in exposed COVID-19 individuals.•A positive response in the DTH in a large part of the patients have strong correlation with the specific anti-RBD IgG test.•DTH seems to have clinical correlation with disease severity.•Highly specific test with no positive DTH results in non-exposed individuals.