There are a lot peer reviewed papers on this topic. Feel free to research them if you'd like. A few studies to google: CDC's January study, although that was

There are a lot peer reviewed papers on this topic. Feel free to research them if you'd like. A few studies to google: CDC's January study, although that wasn't peer reviewed since it's published in MWMR, and those aren't peer reviewed. Israel's large N study on natural immunity compared to not-previously infected, vaccinated population Qatar's study with a sample size of 80,000 (If i recall the sample correctly) Natural immunity conferred greater protection than vaccination alone for Delta. That's clear in these papers. Probably was not the case for previous variants, because the vaccines were generated from the earlier strain. I find it odd that there wasn't a concerted effort to "update" the vaccines with the newer genetic material for the more recent strains. Perhaps it wasn't sensible due to continued mutations inevitable with the virus.