British Prime Minister Boris Johnson announced Wednesday the end of all COVID-19 measures in England that were imposed to combat the highly contagious omicron variant.

Effective immediately, secondary school students will no longer be required to wear face masks in classrooms. Starting next week, masks will not be compulsory anywhere, including on public transport and in shops. However, Johnson said his government will continue to advise people to wear masks in indoor or crowded settings.

The work-from-home guidance will also be lifted next week, along with mandatory COVID-19 passes at large venues, though business are allowed to use them if they wish.

People will still be required to self-isolate after testing positive for COVID-19, but the prime minister said there will "soon be a time" when that won't be mandated. The measure is due to expire in March, but Johnson said that date could be brought forward.

So-called Plan B restrictions were introduced in England last December amid a surge of COVID-19 cases as omicron quickly spread across the United Kingdom. The country's daily number of new cases remains high but appears to be dropping over the past week along with hospital admissions, while deaths are increasing.

Newly reported COVID-19 cases increased 20% last week, the World Health Organization said on Tuesday.

More than 18 million new cases were reported in the week ending Jan. 16, up from about 15 million in the previous week, according to the United Nation's health agency's weekly epidemiological update.

Last week's increase marked a decline from the 55% increase reported the previous week, the agency said.

"Nonetheless, a combination of the increased and rapid spread of the Omicron variant, increased population movements and social mixing during and after the end of year holiday period and challenges with ongoing adherence to public health and social measures (PHSM) are expected to lead to increased number of cases, hospitalizations and deaths in the coming weeks," Tuesday's report said.

About 45,000 new deaths were reported worldwide last week, up from about 43,000 the previous week, the agency said.

The Biden administration will make 400 million non-surgical N95 masks available for free at tens of thousands of pharmacies and community health centers, a White House official said Tuesday.

The administration will start shipping out the masks, which are coming from the Strategic National Stockpile, at the end of this week. Masks will start to be available at pharmacies and community health centers by late next week, with the program "fully up and running" by early February, the official said.

President Joe Biden had announced last week that the administration would be launching a program to provide high-quality masks to Americans for free, but did not provide details.

The announcement comes on the heels of updated guidance from the Centers for Disease Control and Prevention that stated that loosely woven cloth masks provide the least amount of protection against COVID-19, and that Americans in some cases might want to opt for higher quality masks like KN95 and N95 respirators.

-ABC News' Molly Nagle

Three-quarters of all Americans -- nearly 250 million people -- have now received at least one COVID-19 vaccine dose, according to updated data from the Centers for Disease Control and Prevention.

On average, around 296,000 Americans daily are receiving their first shot, down by about 35% since mid-December, federal data shows.

Some 62.7 million eligible Americans -- those ages 5 and up -- are unvaccinated.

-ABC News' Arielle Mitropoulos

Chairman of the Joint Chiefs of Staff Gen. Mark Milley tested positive for COVID-19 on Sunday, according to a statement from Joint Staff spokesman Col. Dave Butler.

Milley has "very minor" symptoms and is working remotely, the statement said.

Milley was last in contact with President Joe Biden on Wednesday.

"He tested negative several days prior to and every day following contact with the President until yesterday," the statement said.

All other Joint Chiefs of Staff tested negative except for Marine Commandant Gen. David Berger, a spokesperson said.

-ABC News' Matthew Seyler