Six months into the drive to inoculate the U.S. population against Covid-19, stark gaps have opened up between the states with the highest and lowest vaccination rates. But so far, states that have been slower to vaccinate haven’t paid a big price in outbreaks of new cases, thanks in part to what scientists call the open-air effect.
Many of the states with the lowest shares of people who have had at least one vaccine shot are located in the Deep South, including Mississippi, Georgia, Alabama and Arkansas, and avoided large outbreaks last spring, only to see cases surge in hot summer months. Most of these states also avoided a spike in cases during the first few months of this year, even as many northeastern states like Vermont, Massachusetts and New Hampshire, which now have some of the highest vaccination rates in the U.S., saw cases rise during the winter and early spring.
Residents in Southern states have largely faced a lower risk of transmission during the winter and spring months because they have been able to spend more time socializing in the open air where the virus disperses more easily, according to epidemiologists and research. And unlike their Northern counterparts, they haven’t had to use heating systems that dry out indoor air. Dozens of studies have shown that the SARS-CoV-2 virus spreads less easily outdoors and in more humid settings.
Doctors and public-health officials worry, however, that as summer approaches, warm-weather states with lower vaccination rates could be vulnerable to a new round of Covid-19 outbreaks as the heat forces people to spend more time in dry, air-conditioned spaces.
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