In Marin County, just over the Golden Gate Bridge from San Francisco, for instance, more than 90 percent of people aged 12 and above have received at least one shot. As a result, Marin has virtually extinguished the virus, with only three new confirmed cases per day in recent weeks.
A second explanation for the new divergence between more and less vaccinated places is the Delta variant. It appears to be making vaccination even more valuable. The vaccines are effective against Delta, sharply reducing the chances of infection and nearly eliminating any chance of serious illness. For unvaccinated people, however, Delta is significantly more contagious than earlier variants.
Missouri offers the clearest example. Over the past week, it has reported more new Covid cases per capita than any other state, and they are concentrated in rural areas that have low vaccination rates, as Charles Gaba, a health care analyst, has noted. In the parts of the state with high vaccination rates — like the metro areas of Kansas City, St. Louis and Columbia — the number of new cases remains very low.
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