COVID-19 updates: US cases down nearly 25%

Pfizer and BioNTech said on Tuesday they have initiated clinical studies to evaluate an omicron-based vaccine for adults. 

The trials will evaluate the "safety, tolerability, and immunogenicity" of the omicron-based vaccine for healthy adults between 18 and 55 years old, the companies said. About 1,400 participants will receive one of three combinations of the companies' current vaccine and the omicron-based vaccine. 

"While current research and real-world data show that boosters continue to provide a high level of protection against severe disease and hospitalization with Omicron, we recognize the need to be prepared in the event this protection wanes over time and to potentially help address Omicron and new variants in the future,” said Kathrin U. Jansen, Ph.D., senior vice president and head of vaccine research & development at Pfizer, said in a statement.

The companies said 615 participants will receive a dose of the omicron booster after two doses of the current vaccine. Another 600 participants will receive a dose of the omicron booster after three doses of the current vaccine. The final 205 participants, who have not been vaccinated, will receive three doses of the omicron vaccine. 

Pfizer and BioNTech said they expected to have initial findings in the first half of 2022. ABC News has also learned Moderna is expected to start similar human trials of an omicron-specific vaccine within the coming days.

-ABC News' Eric Strauss

London police said Tuesday they are investigating parties that allegedly took place at British Prime Minister Boris Johnon's official residence and executive office while England was under strict lockdown because of COVID-19.

In a statement before the London Assembly, Metropolitan Police Commissioner Cressida Dick announced the investigation into "a number of events" at 10 Downing Street.

"The fact that we are now investigating does not, of course, mean that fixed penalty notices will necessarily be issued in every instance and to every person involved," Dick said. "We will not be giving a running commentary on our current investigations."

Johnson is facing growing anger and calls for his resignation over claims he and his staff flouted COVID-19 restrictions imposed by his government. In the latest allegation, ITV News reported that the prime minister attended a surprise birthday party held for him at his office during the first lockdown in June 2020 and later hosted friends in his apartment upstairs that evening. At that time, people in England were barred from meeting more than one individual outside their household.

A spokesperson for Johnson's office called the claim "totally untrue," telling ITV News in a statement that, "in line with the rules at the time, the prime minister hosted a small number of family members outside that evening."

Earlier this month, Johnson acknowledged for the first time that he went to a garden party at 10 Downing Street during the first lockdown in May 2020. While he didn't explicitly admit that he had broken any rules, the prime minister apologized and said he had considered the garden party to be a work event to thank his staff for their efforts during the pandemic.

It was unclear which events London's Metropolitan Police Service is investigating.

Crisis standards of care have been adopted in much of southern Idaho, as hospitals grapple with a surge in COVID-19 patients.

The Idaho Department of Health and Welfare, citing severe staffing and blood supply shortages, activated crisis standards of care on Monday for the southwest, central and south central public health districts, which encompass 18 counties including the Boise, Nampa and Twin Falls metropolitan areas. Crisis standards of care provide legal and ethical guidelines for how health care providers should allocate scarce, life-saving resources, such as ventilators and intensive care unit beds, during an overwhelming public health emergency.

"The highly contagious Omicron variant has thrown us a curve ball," Idaho Department of Health and Welfare Director Dave Jeppesen said in a statement Monday. "Once again, the situation in our hospitals and health systems is dire -- we don't have enough resources to adequately treat patients."

It was the second time amid the coronavirus pandemic that the Idaho Department of Health and Welfare has activated crisis standards of care. Health care rationing was authorized in northern Idaho last September before being extended to the entire state 10 days later. The guidelines were fully deactivated by the end of December.

The latest activation came in response to a request from Saint Alphonsus Health System, which has hospitals in southwestern Idaho as well as eastern Oregon. Jeppesen convened Idaho's crisis standards of care activation advisory committee last Friday, and the committee recommended that the guidelines be activated statewide. Jeppesen decided to only make the designation for southern Idaho, but said other parts of the state will likely be added if current COVID-19 trends continue.

Jeppesen urged residents to get vaccinated and boosted against COVID-19 and to wear high-quality face masks in public places.

"Omicron is so much more contagious than previous variants, and even though a lower percentage of cases are ending up in the hospital, the record number of cases is still putting strain on our healthcare system," he said.

More than 1.1 million children tested positive for COVID-19 last week -- nearly five times the rate of the peak of last winters’ surge, according to a report from the American Academy of Pediatrics and the Children’s Hospital Association.

A total of 10.6 million children have tested positive since the onset of the pandemic. A fifth of those children -- over 2 million kids -- tested positive in just the last two weeks, according to the two organizations.

Pediatric cases in the Northeast are seeing a dramatic drop but new cases in the West, South and the Midwest are still surging.

But there is positive news: COVID-19-related hospitalizations among children fell this week for the first time in one month.

More than 28.4 million eligible children remain unvaccinated.

-ABC News' Arielle Mitropoulos