"We are starting to plateau [at] about 60,000 to 70,000 cases a day. When you have that much viral plateau it almost invariably means that you are at risk for another spike," Fauci said at the daily White House COVID-19 Task Force briefing.
Fauci said three previous peaks in the pandemic ended with new coronavirus cases plateauing at unacceptably higher rates - 20,000 in the spring, 40,000 in the summer, and 60,000 to 70,000 today - a trend he blamed on premature easing of restrictions.
The latest baseline "favors the mutation and the evolution of variants," as the virus undergoes a "selection process" to protect itself from antibodies produced by vaccines and earlier infections, he said.
The drop in new cases from about 250,000 in early January to the present level has prompted more than half of US states to ease, and in some cases completely end, existing restrictions, according to media reports.
Vaccines have been shown to be less effective against variants that have emerged thus far - from Brazil and South Africa - with vaccine manufacturers scrambling to create variant-specific booster shots or new vaccines, according to Fauci.