Five states, including Michigan, are reporting nearly half of the new coronavirus infections in the US, and a top Biden administration health official said Monday that Michigan can't vaccinate its way out of the biggest surge in the US and needs to shut down again.

Michigan recorded more than 100,000 active cases in the last week. The Centers for Disease Control and Prevention (CDC) currently lists it as having the highest infection rate in the country with 492.1 positive infections per 100,000 people.

Hospitals in Michigan also reported a 30 percent rise in COVID-19 admissions over the last week, as the state has seen a dramatic spread of the virus' B-117 variant, with 70 percent of new cases stemming from that strain.

Governor Gretchen Whitmer has said that she won't roll back relaxed coronavirus measures, which currently allow restaurants to be open at 50 percent capacity and schools to hold in-person learning.

She has urged residents to avoid both activities for the next two weeks, but made clear that "these are not orders, mandates, or requirements", while asking the White House for a greater allocation of vaccine doses.

But Dr Rochelle Walensky, CDC director, said Monday at a White House news conference: "The answer is not necessarily to give vaccine. I think if we tried to vaccinate our way out of what is happening in Michigan, we will be disappointed that it took so long for the vaccine to work — to actually have the impact.

"The answer is to really close things down, to go back to our basics, to go back to where we were last spring, last summer, and to shut things down, to flatten the curve, to decrease contact with one another, to test to the extent that we have (people) available to contact-trace," Walensky said.

During the first week of April, 453,360 new coronavirus cases were reported in the US. Five states — New York, New Jersey, Pennsylvania, Florida and Michigan — accounted for 44 percent of new cases, or nearly 197,000, according to data compiled by Johns Hopkins University.

Meanwhile, Regeneron Pharmaceuticals said Monday it will seek Food and Drug Administration (FDA) approval for its COVID-19 antibody drug as a preventative treatment after a trial showed it reduced the risk of symptomatic infections among people exposed to the virus.

If approved, the drug could provide an effective defense for people who are exposed to the virus but aren't vaccinated.

The drug already has been authorized by the FDA to treat mild-to-moderate COVID-19 in people who are at high risk of severe disease.

"With more than 60,000 Americans continuing to be diagnosed with COVID-19 every day, the REGEN-COV antibody cocktail may help provide immediate protection to unvaccinated people who are exposed to the virus," said Dr George Yancopoulos, president and chief scientific officer at Regeneron, in a statement released Monday.

"We are also working to understand its potential to provide ongoing protection for immunocompromised patients who may not respond well to vaccines," he said.

REGEN-COV is a cocktail of two monoclonal antibodies, molecules made to mimic the antibodies produced naturally when the immune system fends off the virus.

The antibody cocktail treatment gained attention last October after it was given to former President Donald Trump shortly after he was diagnosed with COVID-19 last year. The treatment first received emergency authorization from the FDA in November.