Past Covid infection protected against delta, but vaccines safest to prevent dire illness, CDC says NBC NewsWhen the Delta variant dominated, vaccination and prior infection protected against Covid-19, but vaccination was safest, study finds CNNPrior infection, vaccines provide best protection from COVID Yahoo NewsADHS report shows unvaccinated at 17.5 times greater risk of COVID hospitalization KTAR.comVaccination protects against Covid-19 hospitalization more than prior infection CNN