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1/ This paper is the first significant evidence that recent infection with a common cold coronavirus could have a functional cross protective effect against severe COVID-19. “Recent endemic coronavirus infection is associated with less severe COVID-19"
https://www.jci.org/articles/view/143380
https://www.jci.org/articles/view/143380
2/ The possibility of pre-existing (partial) immunity to COVID-19 has been a hot topic. The presence of cross-reactive memory T cells in a fraction of the population opened the possibility of some degree of pre-existing immunity in the population. https://www.nature.com/articles/s41577-020-0389-z
3/ Cross-reactive T cells can provide some degree of protective immunity in flu (Sridhar et al., 2013; Wilkinson et al., 2012). The different ways in which such immunity may manifest for SARS-CoV-2 infection are discussed in: https://www.nature.com/articles/s41577-020-00460-4
4/ Epidemiological evidence from a large cohort of 1,800 people in Massachusetts now supports the possibility of some degree of pre-existing immunity (Sagar et al., 2020). https://www.jci.org/articles/view/143380
5/ SARS-CoV-2 infected individuals with a laboratory confirmed HCoV infection (common cold coronavirus) within the previous three years were at significantly lower risk for ICU admission, after controlling for age and other factors.
6/ Notably, the subjects did not have evidence of protection from infection itself. Instead there was evidence of protection from severe disease. Consistent with some of the crossreactive memory models we considered.
7/ Firmer evidence will likely require pre- and post-infection T cell measurements with clear distinctions of individuals who have been exposed to SARS-CoV-2, but this epidemiological study is a strong contribution to the literature.
