Natural immunity better protects against the Delta strain of COVID-19 than a vaccine, according to a study released by the Centers for Disease Control and Prevention (CDC) on Wednesday.

Researchers examined COVID-19 cases and hospitalizations from May through November 2021 in California and New York. The research team examined case and hospitalization rates among four cohorts of people: the unvaccinated and previously uninfected, the vaccinated and previously infected, the unvaccinated with a previous COVID-19 diagnosis, and the vaccinated with a previous COVID-19 diagnosis.