Previous infection with the coronavirus appeared to provide stronger protection against the Delta variant than did vaccination in a large sample of patients, the Centers for Disease Control and Prevention reported. Scientists analyzed testing, surveillance and immunization data from the [New York and California] to gauge the level of protection offered by vaccines and previous infection. During the week beginning May 30, 2021, vaccinated people who had not experienced Covid had the lowest risk of coronavirus infection and hospitalization, followed by unvaccinated people who had been previously diagnosed with Covid. By the week beginning Oct. 3, however, vaccinated people with a prior diagnosis fared best against the Delta variant. Unvaccinated people with a history of Covid also had lower rates of infection and hospitalization than those protected by vaccines alone. Waning of vaccine-derived immunity may explain why vaccinated people were less protected from infection with the Delta variant than those who had a prior diagnosis. A recent study of employees at the Cleveland Clinic suggested that ... vaccination does not add much benefit to a prior bout for the first many months.