Anna Moneymaker-Pool/Getty Images

The head of the Centers for Disease Control and Prevention is warning the United States must take action to prevent an another "avoidable" surge of COVID-19 cases.

CDC director Rochelle Walensky during a briefing Monday expressed concern over the "apparent leveling off of cases and hospital admissions" in the United States after previous consistent declines, also noting that some states are seeing an uptick in new cases.

Walensky described states rolling back COVID-19 restrictions, despite cases remaining high and while COVID-19 variants spread, as a "serious threat to the progress we have made" in the pandemic so far.

"We must find the fortitude to hang in there for just a little bit longer," Walensky said. "We are at a critical point in this pandemic, a fork in the road where we as a country must decide which path we are going to take. We must act now, and I am worried that if we don't take the right actions now, we will have another avoidable surge, just as we are seeing in Europe right now, and just as we are so aggressively scaling up vaccination."

As the CDC raises concerns about the possibility of another surge, though, other experts have argued a significant one might not be likely. Former FDA commissioner Scott Gottlieb said Sunday that "I don't think we're going to have a fourth wave," though there could be "plateauing for a period of time." CNN's Sanjay Gupta similarly said Monday that especially given the level of immunity in the United States as COVID-19 vaccines continue to roll out, "I think it's unlikely, frankly when you just look at the data, that we're going to have a significant fourth surge."