The study did not explain why protection against reinfection and hospitalization grew among those individuals with a prior infection during Delta.

The study, published Wednesday, looked at four categories of people in New York and California -- individuals who were unvaccinated with and without a prior infection and vaccinated people with and without a prior infection.
[...]
Eli Rosenberg, deputy director for science at the New York State Department of Health who helped with the study, said "the totality of the evidence suggests ... that both vaccination and having survived Covid each provide protection against subsequent infection and hospitalization." "Either of those provides protection, and only one of those is the safe choice that we would recommend. And that's vaccination," he said.

Protection against Delta was highest, however, among people who were both vaccinated and had survived a previous COVID infection, and lowest among those who had never been infected or vaccinated, the study found.

well, alrighty then
archivedSCOTUS oral argument, NFIB v. Dept. of Labor

JUSTICE SOTOMAYOR: Others, unvaccinated people at risk and people who are vaccinated. They may be at a lesser risk, but the grave risk remains to people of all ages and conditions that are unvaccinated.
MR. FLOWERS: Right, but -- but the problem is they've defined numerical probabilities that are equal to be grave in one case and not grave in the other, and that is the definition of irrational.