The decline in COVID preceded vaccines. But we need jabs to finish the job.

By mid-February 2021, an estimated 150 million people in the U.S. (30 million times five) may have had been infected with SARS-CoV-2. By April, I estimated the natural immunity rate to be above 55% in 10 states: Arizona, Iowa, Nebraska, North Dakota, Oklahoma, Rhode Island, South Dakota, Tennessee, Utah, and Wisconsin. At the other end of the continuum, I estimated the natural immunity rate to be below 35% in the District of Columbia, Hawaii, Maine, Maryland, New Hampshire, Oregon, Puerto Rico, Vermont, Virginia, and Washington. The table below summarizes how these two groups of states with high and low natural infection rates differ. By the end of 2020, new infections were already rapidly declining in nearly all of the 10 states where the majority may have had natural immunity, well before more than a minuscule percentage of Americans were fully vaccinated. In 80% of these states, the day when new cases were at their peak occurred before vaccines were available. In contrast, the 10 states with lower rates of previous infections were much more likely to experience new upticks in Covid-19 cases in March and April. The date with the highest number of new cases occurred before vaccines were available in only 30% of these states. By the end of May, states with fewer new infections had significantly lower vaccination rates than states with more new infections.