@babbaloushka
Several studies have now shown that immunity after natural infection persists for over 6 months in the majority of people and that reinfection is rare.
Five studies were identified that reported low rates of SARS-CoV2 reinfection up to seven months following initial infection. Additionally, a scoping review of the long-term duration of immune responses found that while there may be a waning of antibody responses over time, T- and B-cell responses persist for up to eight months post-infection. Source
About 95% of subjects retained immune memory at ~6 months after infection.
Source
One of the most significant findings of the study is that 99% of participants who had tested positive for previous infection retained antibodies to SARS-CoV-2 for 3 months after being infected, and 88% did so for the full 6 months of the study.
Source
Even mild/asymptomatic infection can produce lasting immunity:
In conclusion, despite concerns of waning immunity, appropriate immunoassays can detect antibodies against SARS-CoV-2 at 8 months after infection in most asymptomatic or mildly symptomatic persons.
Source
Immunity can wane faster in the older population source but the same may also be found for vaccine induced immunity, we don't really have that data yet. Boosters may be needed more frequently in these groups.
Vaccine induced immunity to viruses does not always offer greater protection than natural infection. For example, pertussis Source and mumps source.
Yes, the vast majority of reinfections are milder - just as people who are infected after having the vaccine are more likely to have a mild version of the disease(see previous links). However, there have also been people who have died despite having been vaccinated.
@FourOnTheHill I hope you find some of this information helpful too