Natural Immunity Can Exist Prior to SARS-COV-2 Infection

Healthy people have pre-existing T-helper cell and cytotoxic T-cell immunity to the SARS-Coronavirus prior to infection. This is one of several studies to find that healthy people can have per-existing T cell immunity to the SARS-Coronavirus even before they are exposed.

Source: Nature

Peripheral blood mononuclear cells sampled from US donors between 2016 and 2018 and Indian donors between 2015 and 2017 (n = 14) had a strong cytotoxic T-cell mediated interferon gamma response to 11 different epitopes of the SARS-Coronavirus spike protein, simulated by a peptide mix, within 2 days with the maximum response detected after 7 days. The authors note that prior experimental research has found that healthy participants had pre-existing T cell immunity to the SARS coronavirus using spike protein peptides likely due to cross-reactive T cell receptors created from exposure to other coronaviruses. This kind of research explains why so many people had asymptomatic infections, which was estimated to be around 40-50% in 2021 before most people had even been exposed to the virus.