Coronavirus deaths in the U.S. are on the rise once again.

The average number of deaths per day is up 10% over the last two weeks, the Associated Press reported, citing data from Johns Hopkins University. As of Sunday, deaths were up from 721 to nearly 794.

Overall, deaths have increased in some 34 states, with daily new cases on the rise in nearly all 50 states. (iStock)

Overall, deaths have increased in some 34 states, with daily new cases on the rise in nearly all 50 states.

When cases rise, mortality rates often do as well, according to experts. Deaths are a lagging indicator — that is, it generally takes a few weeks for people to sicken and die from the coronavirus. Earlier this month, the World Health Organization (WHO) warned of a mortality spike in connection with a global spike in virus cases.

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One infectious disease expert with the University of Minnesota blamed the spike in cases on three main factors: “Pandemic fatigue" among people who are weary of hunkering down and are venturing out more; “pandemic anger” among those are don’t believe the scourge is a real threat; and cold weather, which is forcing more Americans indoors, where the virus can spread more easily.

“When you put those three together, we shouldn’t be surprised what we’re seeing,” Michael Osterholm, a University of Minnesota expert on infectious diseases, told the AP.

Deaths are still well below the U.S. peak of over 2,200 per day in late April. But experts are warning of a grim fall and winter, with a widely cited model from the University of Washington projecting about 386,000 dead by Feb. 1. A vaccine is unlikely to become widely available until mid-2021.

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The seven-day rolling average for daily new cases hit a record high on Sunday of 68,767, according to Johns Hopkins, eclipsing the previous mark of 67,293, set in mid-July. The U.S. recorded more than 80,000 new cases on both Friday and Saturday — the highest marks ever — though testing has expanded dramatically over the course of the outbreak, making direct comparisons problematic.

The true number of infections is thought to be far higher because many Americans have not been tested, and studies suggest people can be infected without feeling sick.

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The news comes after a recent report from the Centers for Disease Control and Prevention (CDC) found that the coronavirus is behind two-thirds of the almost 300,000 higher-than-average U.S. deaths this year.

Fox News’s Kayla Rivas and the Associated Press contributed to this report.