In line with expectations, all 23 individuals who recovered from severe COVID-19 developed both SARS-CoV-2 specific antibody and T cell responses.

But surprisingly, SARS-CoV-2 specific memory T cell responses were detected months after infection in exposed family members and in most individuals with a history of very mild COVID-19, sometimes in the absence of SARS-CoV-2 specific antibodies.

Among the 31 individuals who recovered from mild COVID-19, almost all had detectable antibody responses (27/31) and developed T cell responses (30/31).

“Our findings suggest that the reliance on antibody responses may underestimate the extent of population-level immunity against SARS-CoV-2,” Buggert said.

“The obvious next step is to determine whether robust memory T cell responses in the absence of detectable antibodies can protect against COVID-19 in the long term,” the author noted.