"Conclusions This study demonstrated that natural immunity confers longer lasting and stronger protection against infection, symptomatic disease and hospitalization caused by the Delta variant of SARS-CoV-2, compared to the BNT162b2 two-dose vaccine-induced immunity. Individuals who were both previously infected with SARS-CoV-2 and given a single dose of the vaccine gained additional protection against the Delta variant."
Much of this discussion, including to a significant degree this study, rate immunity using a linear metric based on detection of infections. A more nuanced view of the situation shows that vaccine immunizations cause a very strong immune reaction to the particular viral components in the vaccine while natural immunity tends to cause immune reactions that are not as strong but cover more if not all of the exposed virus components.<p>Having weaker but more general immunity would potentially explain why natural immunity was better able to handle a new variant. This does not eliminate the possibility that a new booster deliberately designed to counter all current variants may be even more effective.<p>In particular that is true for the Delta. The Delta variant is so virulent that it currently dominates by a wide margin over all other variants and there is not necessarily going to be a more virulent variant. This means that the current problem is quite likely not to be ready for more variants, but to focus on handling the Delta variant. That in turns means that vaccines and vaccine boosters may be called for as the best possible option even though natural immunity may be helpful. Natural immunity also comes with far greater risks which is another reason to focus on vaccines and boosters.