As COVID-19 cases creep up again across the country, federal officials and epidemiologists say they're worried we could hit another tipping point, leading to a fourth significant surge of infections, hospitalizations and deaths.

"We're skating on a knife's edge right now," said Nicholas Reich, a biostatistician at the University of Massachusetts Amherst.

Average daily reported cases are up 10% compared to a week earlier, data from the Centers for Disease Control and Prevention shows, with more than 30 million COVID-19 cases reported since early last year. Hospitalizations and deaths, which usually lag cases by a few weeks, have inched upward as well, after a decline and plateau that began in early January.

Reich and others say they expect that the immunity from natural infections plus the successful rollout of vaccines, which are now reaching nearly 3 million people a day, will help moderate this surge.