I thought the most recent study said that prior Covid infection does not offer as much immunity as the vaccine does. This was posted here also.
The unanswered question is how much that's protective against future infection. Nobody really knows. Antibodies are an important part of the immune system, but the real key for long-term protection is the effect on memory T-cells. I'm not aware of any studies on that topic.
"To summarize:
- Antibodies decrease but memory B/T cells are stable for ≥6 mo
- Immune memory is still effective vs. variants
- "Boosting" from memory = significant (but temporary) increase in antibodies w/ less impact on already durable memory cells"