I was very skeptical of it as well, and had the same reaction to the medical professionals saying this. Their off the cuff "oh, yeah, ninety days, makes sense" led to me believe them. Note as well I'm referring only to catching covid - not the vaccine.

There's this early study from July as well https://www.nejm.org/doi/full/10.1056/NEJMc2025179?query=fea...

And cdc guidance https://www.nbcnews.com/health/health-news/cdc-suggests-reco...