US sees rise in COVID-19 cases during summer months, experts say
Health officials report a summer increase in COVID-19 infections across most states, noting that the trend follows a pattern of biannual waves and is driven by behavioral factors and waning immunity.
COVID-19 cases are climbing nationwide as summer progresses, according to federal and academic monitoring systems. The Centers for Disease Control and Prevention estimates that infections are growing or likely growing in 47 states, with the South and West showing the strongest increases, said Dr. Syra Madad, an infectious-disease epidemiologist at Harvard’s Belfer Center.
Data from WastewaterSCAN, a Stanford University-led wastewater surveillance program, indicate that viral concentrations in August were 105% higher than in July and have doubled each month since June. "Since we began monitoring COVID-19 in wastewater, we have seen a similar pattern: virus concentrations peak in the summer and winter months," explained Amanda Bidwell, the program’s scientific manager.
The CDC’s COVID-NET hospitalization tracker also shows a consistent rise in cases beginning in July and lasting through September, a pattern described as a "summer wave" by experts. Dr. Michael Mina, chief medical officer at Invivyd, noted that the timing of the upswing has been practically identical each year since the pandemic began.
Researchers attribute the seasonal pattern to a combination of environmental and behavioral factors. Higher indoor occupancy in air-conditioned spaces during hot weather and increased contact among schoolchildren in late summer are cited as contributors. Dr. Andrew Handel of Stony Brook Children’s Hospital added that the emergence of new variants and waning immunity after six months also elevate risk of breakthrough infections.
While emergency-department visits remain low, officials caution that older adults, infants and immunocompromised individuals remain vulnerable. Madad emphasized proportionate vigilance, recommending testing when symptomatic, improving ventilation, maintaining good hygiene, consulting health providers about antivirals, and using well-fitted masks around vulnerable people.
Public health experts suggest that expanding immunity through vaccination and natural exposure could reduce the magnitude of future summer waves, but they stress continued use of existing preventive measures to limit transmission and severe disease.