New weekly COVID-19 hospitalizations increased more than 20% in early August, according to the most recent data from the Centers for Disease Control and Prevention.

The week ending in Aug. 12 saw more than 12,600 new coronavirus hospital admissions – a jump of nearly 22% of the previous week.

While hospitalizations are not close to previous peaks during other COVID-19 surges, it’s still the first wave since winter. Experts say the summer increase isn’t a surprise but that it should be a wake-up call to treat the virus seriously before winter rolls around.

The vast majority of U.S. counties are documenting a “low” level of new COVID-19 hospital admissions. Less than 3% of counties are seeing a “medium” level, according to CDC data. None are experiencing a “high” level of admissions.

The CDC no longer tracks COVID-19 infections, but researchers say the spread is likely significant given the increase in hospitalizations. Deaths, which tend to lag behind hospitalizations, have not yet shown a similar increase.

EG.5, or “eris,” is the most prominent coronavirus strain circulating in the U.S. It’s responsible for more than 20% of new infections in recent weeks, according to CDC data.

Another new strain – BA.2.86 – prompted quick reactions from the CDC and the World Health Organization last week. The strain, which has over 30 mutations, is not common enough to make it onto CDC’s variant tracker, but it has been found in very small numbers in the U.S., the U.K., Denmark and Israel.

A CDC spokeswoman told U.S. News in a statement that “scientists are working now to understand more about the newly identified lineage and we will share more information as it becomes available.”