Covid reinfections: are they milder and do they strengthen immunity?

It's reasonable to assume that, in general, reinfections should be less severe than primary infections, as the person being reinfected will have some pre-existing immunity from their primary

We’ve known since early on in the pandemic that COVID reinfections could occur. One of the first reinfections reported was in a 33-year-old man from Hong Kong. His initial infection was diagnosed on March 26 2020, with his second infection, with a genetically distinct virus, being diagnosed 142 days later.

Since then reports of reinfection have become common, especially since the emergence of the omicron variant. Early research from South Africa (still in preprint, so awaiting review by other scientists) suggests that the risk of reinfection increased quickly and substantially after the variant arrived.

So why are reinfections increasing? The simple answer