“Overall, the people who’ve been coming through with Covid are much, much less sick than they were even this winter,” said Dr. Megan Ranney, an emergency physician at Brown University. “It feels like almost a different disease for folks, with the exception of people who are really old, who are unvaccinated or who are immunosuppressed.”

Disparities in access to booster shots and antiviral pills have also put some Americans at higher risk. Black and Hispanic people eligible for boosters have received the shots at lower rates than white people have, reflecting what some epidemiologists describe as limited efforts in some states to put boosters within easy reach. Patients who do not have primary care doctors, or who live far from pharmacies, can also struggle to get antiviral pills.

The number of hospitalized Covid patients is still climbing nationally, making it likely that increases in deaths will gradually follow, epidemiologists said. It is unclear how hard the wave will hit less-vaccinated regions, like the South, where immunity from past infections has also grown.

“Unfortunately, vaccination rates in many southern states are among the lowest in the country,” said Jason Salemi, a professor of epidemiology at the University of South Florida. “But there is certainly a lot of immunity built up through prior infection.”

Even as fewer cases turn deadly, the unprecedented number of infections this winter and spring has created significant problems of its own. In the United States, one in five adult survivors of Covid under 65 has dealt with some version of long Covid, a recent study found. Many people have missed work, including doctors, whose absences this spring have periodically strained hospitals that already had staffing problems.

Dr. Karan, of Stanford, said that he had lingering symptoms from a January bout with Covid until April. A month later, he was infected again. As of last week, he said, with the subvariant surge hitting California, his team of five doctors at one of the hospitals where he works had been reduced to two because of Covid absences, forcing delays to consultations for some patients.