Past infection with viral pathogens that are closely related to covid-19 may provide limited protection against covid-19.
https://www.nytimes.com/2020/08/06/health/coronavirus-immune-cells.html?referringSource=articleShare
https://www.youtube.com/watch?v=WbG6mzYUnyU&feature=youtu.be&fbclid=IwAR07cSRiUzBpr1LyW6_XXDtifWuQI9z0N3RTdP37Hv9HXv6oyu1qvRAe1gg