During America's last surge of the coronavirus driven by the Delta variant, people who were unvaccinated but survived Covid were better protected than those who were vaccinated and not previously infected, a new study said Wednesday.

The finding is the latest to weigh in on a debate on the relative strengths of natural versus vaccine-acquired immunity against SARS-CoV-2, but comes this time with the imprimatur of the US Centers for Disease Control and Prevention (CDC).