It’s both. Vaccines helps give the immune system the genetic information to pinpoint the exact way to make antibodies specific to fight off Covid.

The natural immune system without vaccines first launches a generalized response against it because the body doesn’t have the blueprint for what antibodies to produce yet. So this gives the virus a head start and a longer time window to successfully reproduce inside your body and infect more of your organs since it appears it can affect multiple systems and not just one area (such as the cold virus staying mostly in the upper respiratory area).

Vaccination lets the body direct a more effective attack and a faster response to infection so this gives the patient a much better chance at avoiding severe infection and will shorten recovery. Vaccines don’t prevent infection but they do allow a rapid immune response that should effectively kill off the virus to make the infection short lived and not severe.

At the same time these newer strains SHOULD (this is no guarantee but generally a virus that doesn’t kill its host is more successful since it can spread more widely) become less lethal. And this SHOULD continue as a trend. The disclaimer being that just like with the flu, you could see the appearance of a evasive strain that has a high lethality trait too just as we saw with the 1917 Spanish flu epidemic.