[oskarpearson]

For the same reason most vaccines require two doses. And for the same reason some countries are planning or doing booster shots.

Antibody levels drop rapidly after an infection, if they persist at all.

Getting a vaccination after infection re-triggers the immune system and makes antibodies more likely to persist for longer.

Reading up on this many months ago it seemed likely that natural infection plus a single vaccination would be equivalent to two vaccine shots.

There was research about only needing to give one shot of vaccines like AstraZeneca to people with previous infection. It was considered too complex to manage, and the research as to efficacy wasn’t finalised, so they stuck with two.

Having had Covid, plus two shots of something like AstraZeneca is presumably somewhere in the region of a standard two-shot-plus-booster campaign.

I don’t really understand much of this paper, but given other comments it seems to be a reasonable idea.