about a year ago a study was done where they tested known people that were infected with the SARS2 virus in 2002-2003 and they found ALL of them had T-Cell immunity that worked for the Fauci Flu also because of it’s close relation.
Here’s a per reviewed paper on that long lasting SARS immunity: https://www.nature.com/articles/s41586-020-2550-z_reference.pdf