[set fair (OP)]

The classic explanation we have obout how vaccines work includes something like "so that our immune system knows how to deal with a real infection when it arrives?" But there is also, levels of antibodies remaining at the time of actual infection. Do we know which - memory or extant antibodies are more important with covid? Is there any evidence that memory is involved?

[evan_au]

Both are important.
- But antibodies are (a bit) easier to measure

Antibody levels decline over time, so memory cells are important for long-term protection (provided the virus does not mutate significantly).
- But during an infection, antibody levels rise: antibodies ideally disable virus particles from entering cells; they also mark virus particles for destruction.
- Killer cells identify human cells that have been taken over as virus factories, and shut them down (with extreme prejudice)