Science reports:

The natural immune protection that develops after a SARS-CoV-2 infection offers considerably more of a shield against the Delta variant of the pandemic coronavirus than two doses of the Pfizer-BioNTech vaccine, according to a large Israeli study that some scientists wish came with a “Don’t try this at home” label. The newly released data show people who once had a SARS-CoV-2 infection were much less likely than vaccinated people to get Delta, develop symptoms from it, or become hospitalized with serious COVID-19.

The study demonstrates the power of the human immune system, but infectious disease experts emphasized that this vaccine and others for COVID-19 nonetheless remain highly protective against severe disease and death. And they caution that intentional infection among unvaccinated people would be extremely risky. “What we don’t want people to say is: ‘All right, I should go out and get infected, I should have an infection party.’” says Michel Nussenzweig, an immunologist at Rockefeller University who researches the immune response to SARS-CoV-2 and was not involved in the study. “Because somebody could die.”

The researchers also found that people who had SARS-CoV-2 previously and then received one dose of the Pfizer-BioNTech messenger RNA (mRNA) vaccine were more highly protected against reinfection than those who once had the virus and were still unvaccinated. The new work could inform discussion of whether previously infected people need to receive both doses of the Pfizer-BioNTech vaccine or the similar mRNA vaccine from Moderna. Vaccine mandates don’t necessarily exempt those who had a SARS-CoV-2 infection already and the current U.S. recommendation is that they be fully vaccinated, which means two mRNA doses or one of the J&J adenovirus-based vaccine. Yet one mRNA dose might be enough, some scientists argue. And other countries including Germany, France, Italy, and Israel administer just one vaccine dose to previously infected people. [Continue reading…]