I live with my partner. He was very sick for a few days (and tested negative, which I think was false) and I was not sick at the time. It then got me very sick a few days later, where I tested positive.

So now we're both feeling awful, but he's on the come-up on feeling better. However, he wakes up this morning feeling horrible in a way that feels different than before and he thinks I reinfected him.

Is this possible? From the beginning of the pandemic to now, we thought immunity lasted anywhere from 3 months to now being at LEAST a few weeks. Can you be reinfected just like that? We have both been vaccinated in the past, I got my booster less than a year ago, neither of us are immunocompromised.

Edit: Another thought he had was that he didn't initially have covid and was just sick, I did have covid (and still do), and he then got sick with 2 things in a row.