The study, published on Wednesday by the US Centers for Disease Control and Prevention (CDC), found that as the Delta variant became the dominant coronavirus strain during the second half of 2021, people who were vaccinated were six times less likely to catch Covid-19 than those who hadn’t been jabbed.
However, those who had been infected with an earlier variant of the coronavirus, but hadn’t been vaccinated, were between 15 and 29 times less likely to catch the virus.
A similar difference was noticed in hospitalization rates, with prior immunity conferring better protection against hospitalization than vaccination.
Despite its disadvantage compared to natural immunity, the CDC stressed that “vaccination remains the safest strategy” for preventing Covid-19 infections. This is because "having Covid the first time carries with it significant risks,” study co-author Dr. Eli Rosenberg told CNN. Likewise Dr. Erica Pan, state epidemiologist for the California Department of Public Health, recommended that even those with prior infection get vaccinated to ensure they get a layer of “additional protection.”
The study’s conclusion contradicts earlier claims from top US health officials. At the beginning of the Delta outbreak last May, White House Chief Medical Advisor Dr. Anthony Fauci insisted that vaccines “are better than the traditional response you get from natural infection." Fauci has also been accused by Republican lawmakers of ignoring studies touting the benefits of natural immunity, “because it foils his plans to get everybody possible vaccinated.”
As it was conducted during the surge of Delta infections, the study offers no insight into the efficacy of vaccines against the now-dominant Omicron variant.