Some studies that infection actually may make it easier to catch it again
https://www.science.org/doi/10.1126/science.abq1841
and that covid causes immunological dysfuction even 8 months later
https://www.science.org/doi/10.1126/science.abq1841
and that covid causes immunological dysfuction even 8 months later
https://www.medrxiv.org/content/10.1101/2022.12.17.22283625v...
See Figure 2 (end of the paper). Preprint, but pretty straightforward census of hospital staff.