It's a good question.
Cold weather was commonly cited as a contributing factor to previous upturns in COVID-19 infections, inviting curiosity about extreme heat's influence on the current uptick, according to Bloomberg.
COVID-19 hospitalizations in the U.S. rose 43 percent in the last week in July from a low in the week ending June 24, according to CDC data. There were 9,056 new COVID-19 hospitalizations for the week ending July 29, marking a 12.5 percent jump from the week prior. New Hampshire, Vermont, Kansas and South Dakota saw the greatest climbs in hospitalizations in that time.
Coincidentally, July 2023 marked Earth's hottest month on record, with heat spilling over into August. In the U.S., prolonged heat waves have blanketed large swaths of the country and likely drove people to spend more time indoors, which could give COVID-19 more opportunities to spread.
But correlations do not spell causation, and experts are encouraging caution before making the link of air-conditioned gatherings to the recent upward swing of COVID-19 cases.
Michael Osterholm, PhD, director of the Center for Infectious Disease Research and Policy at the University of Minnesota in Minneapolis, told Bloomberg he has been critical of reasoning that attributes COVID-19 surges to changes in human behavior and there is more to learn about the ecology of viruses. For instance, even when COVID-19 cases increased in the winter, they often declined well before the weather changed enough to allow more outdoor activities.
There is also a data vacuum, with little evidence that people are spending much more time indoors now than they were in spring, or evidence that most people ever spend enough time outside to affect the global patterns of respiratory viruses.
Access to COVID-19 vaccines has been reduced as the U.S. stopped purchasing them from drugmakers for the public, and protection is waning for those who were immunized months ago — whether through vaccination or contracting the virus. The new COVID-19 strain, EG.5, recently became the most prevalent in the U.S., but there's no evidence that it spreads more easily than its predecessors, a CDC spokesperson told Bloomberg.
More broadly, it's not clear whether COVID-19 will continue to tick upward every summer. 2023 marks the fourth year it's done so, but it's possible that waning immunity and new variants have created the appearance of a pattern.