The United States death toll from COVID-19 topped 4,000 for the first time on Thursday, setting yet another daily world record, as top public health official Dr. Anthony Fauci warned the U.S. outbreak will get even worse in the weeks ahead.

Arizona is now one of the worst-affected parts of the world, with nearly 1% of state residents testing positive for coronavirus in just the past week.

In California, the National Guard is assisting the Los Angeles County Coroner’s Office, after morgues and mortuaries ran out of storage space for COVID-19 victims.

The CDC reported Thursday that asymptomatic carriers of coronavirus are responsible for more than half of new infections — a finding that bolsters the urgent need for masks and social distancing. Meanwhile, new research published in the journal Science Immunology shows about nine out of 10 people have robust immunity to coronavirus eight months after an infection. It’s not yet known if immunity wanes after a longer interval.