How Covid-19 migrated across America

The spread of the Omicron variant across the United States threatens to increase cases as many people head indoors in cold weather. It turns out that the season seems to play a big role where Covid-19 strikes the most.

On Monday, the Centers for Disease Control and Prevention said the Omicron variant had supplanted Delta as the dominant strain in the United States.

The shape of that latest wave is still in question, but nearly two years of data have revealed some geographic trends for the pandemic. Spring disproportionately affected the northern states. Summers have been the harshest in the South.

Weighted average latitude of confirmed cases of Covid-19 in the continental United States

Weighted average latitude of confirmed

Cases of Covid-19 in the continental United States

Weighted average latitude of confirmed

Cases of Covid-19 in the continental United States

Outdoor temperatures have been one explanation: The summer heat in the south sends more people indoors, where transmission is more likely to occur, while residents of northern states are more likely to be indoors. exterior, which mitigates the spread. Colder weather in much of the United States, combined with the arrival of Omicron, could increase the number of cases this winter.

One unknown this winter season is how well-vaccinated places behave compared to less-vaccinated states. Vaccines were developed to protect against serious disease, and before Omicron’s arrival, vaccination rates were also correlated with lower case rates. The picture is more muddled now, as infection rates rise even in states with high vaccination rates.

Vaccination rate in relation to cases and deaths,
by state

While the correlation between state immunization rates and deaths is weaker than it was just a few months ago, health experts say in part that even the states with the highest immunization rates high have a large number of unvaccinated people.

Philip Landrigan, an epidemiologist who heads the Program for Global Public Health and the Common Good at Boston College, cites Massachusetts as an example, where more than 80% of the population has received at least one dose of the vaccine. But, he says, that still leaves an estimated 1.4 million people unvaccinated.

“The rapid spread of infection and the increasing number of deaths among this large group of unvaccinated people are more than enough to erode the previous progress against the pandemic and weaken the correlation,” said Dr Landrigan.

Data collected by the CDC in about half of all states, representing about 62% of the U.S. population, illustrates the gap. By the end of November, data showed infection rates in unvaccinated Americans were five times higher than in fully vaccinated individuals, and the risk of death was 13 times higher.

Write to Randy Yeip at [email protected]

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