They wrote, “Although laboratory evidence suggests that antibody responses following Covid-19 vaccination provide better neutralization of some circulating variants than does natural infection, few real-world epidemiologic studies exist to support the benefit of vaccination for previously infected persons. . . . To reduce their risk of infection, all eligible persons should be offered vaccination, even if they have been previously infected.”
The researchers said they picked May and June for two main reasons: “When vaccination supplies were low, some previously infected persons were deferring vaccination for 90 days to allow never-infected persons priority for available vaccine; however, by May 2021, deferral for 90 days was no longer a reason for those infected in 2020 to remain unvaccinated. Second, although vaccination eligibility was initially restricted based on age, co-morbidities, and occupation,” all Kentucky residents 16 and older became eligible for vaccination in early April.
The researchers acknowledged limitations of the study, including: Genomic sequencing was not used to confirm that reinfection was caused by the same variant of the virus as the first infection, and vaccinated people “are possibly less likely to get tested,” so “the association of reinfection and lack of vaccination might be overestimated.”