The CDC raised its wastewater thresholds for COVID in August, so a level once classified as “high” transmission may now register as ”moderate,” a change the agency called a routine recalibration that better reflects current risk. Experts said the change makes sense given widespread immunity, while noting that COVID infections are still rising in 27 states.

As fewer people take tests or seek medical treatment for COVID infections, viral activity in wastewater has become a key way to measure transmission, says David Larsen, professor and chair of public health. “The wastewater becomes really essential,” he says.

Read more in the NBC News article, “Why the CDC edited a key COVID metric, and what it says about the state of the virus.” This article may require a subscription.