By Jonathan Levin

Covid-19 transmission is accelerating in several poorly vaccinated states, primarily in the South plus Missouri and Utah, and more young people are turning up at hospitals. The data present the clearest sign of a rebound in the U.S. in months.

In Missouri, Arkansas and Utah, the seven-day average of hospital admissions with confirmed Covid-19 has increased more than 30% in the past two weeks, according to the U.S. Department of Health & Human Services. In Mississippi, the hospitalization rate is up 5% in the period.

The jump in hospitalization is particularly jarring among 18- to 29-year-olds in the outlier states.

An analysis by the genomics firm Helix suggests that the highly contagious delta variant in particular, which has prompted concern worldwide as it leads to new surges of Covid-19 across the globe, is spreading in undervaccinated pockets of the U.S.

The U.S. has made extraordinary progress in its vaccine push, giving at least one jab to more than 53% of the population. But all the states with mounting transmission trail the national average, and Mississippi has given a single jab to just 35%. Young people are less likely to be vaccinated than older groups.

In Arkansas, Missouri and Utah, reported Covid-19 cases mirror the concerning trends in hospitalizations. In other places -- namely, Mississippi -- they don’t. Testing has dropped off significantly, with the seven-day average nationwide plummeting 55% in the past three months, which makes case counts a less reliable indicator.

Most Covid-19 projections expect subdued transmission during the summer, thanks in part to the seasonal nature of the virus. But the so-called Sun Belt surge last year showed that many Southern states can remain vulnerable as hot summer days drive people indoors in search of air-conditioning.

Even for the worst-afflicted states, the situation is nowhere near as alarming as what residents survived as recently as February; absolute numbers of hospitalizations remain far lower. But the signs of an uptick come amid a jump in cases in the U.K. attributed to the spread of the highly transmissible delta variant.