COVID-19 updates: US cases down nearly 25%

Florida Gov. Ron DeSantis has vowed to "fight back" against the U.S. Food and Drug Administration's "reckless" decision to limit the use of two monoclonal antibody treatments for COVID-19 that were found to be ineffective against the now-dominant omicron variant.

"This is wrong what they are doing, and we have many people now who are very concerned because they were going to go in and get it today or tomorrow," DeSantis said during a press conference Tuesday.

While the governor acknowledged that the treatments are less effective against omicron, he claimed that people in Florida have seen their COVID-19 symptoms clear up in the last month after receiving the treatments. DeSantis, however, did not offer data to support that claim.

"We're going to fight back against this," he told reporters.

When asked whether he plans to take legal action against the federal government, DeSantis said: "I don't know. We're going to see what we can do."

With omicron accounting for more than 99% of COVID-19 infections nationwide, the FDA on Monday revised its authorizations for two of the main monoclonal antibody treatments that have been widely used across the country -- one made by Eli Lilly and the other by Regeneron. The FDA said both treatments are no longer authorized for use in any U.S. state, territory or jurisdiction and should not be used for treatment against COVID-19. In the future, the treatments could still be used to help patients who become sick with other variants, according to the FDA.

Following the FDA's decision, Florida health officials announced that monoclonal antibody treatment sites would be shut down across the state. More than 2,000 appointments for the treatments were canceled statewide on Tuesday alone, according to the governor's office.

"Unfortunately, as a result of this abrupt decision made by the federal government, all monoclonal antibody state sites will be closed until further notice," the Florida Department of Health said in a statement late Monday. "Florida disagrees with the decision that blocks access to any available treatments in absence of clinical evidence. To date, such clinical evidence has not been provided by the United States Food and Drug Administration (FDA)."

-ABC News' Will McDuffie and Sasha Pezenik

Kentucky Gov. Andy Beshear's son has tested positive for COVID-19 as cases in the state skyrocket.

"My son is generally asymptomatic, we believe because he is vaccinated and boosted," Beshear said Monday.

The governor and the rest of his family tested negative on Monday, according to Beshear's office.

Kentucky reported 81,473 cases for the week ending on Sunday -- a record high.

Hospitalizations are also approaching a record high, his office said.

The World Health Organization is sounding the alarm over rising cases of a new omicron sub-variant.

In an updated post to its website on Monday, the WHO said the new sub-variant, called BA.2, is a descendant of omicron, the now-dominant, highly contagious variant of the novel coronavirus. Unlike omicron, BA.2 is currently not considered a "variant of concern." But because it is spreading in many countries, the WHO is asking governments and scientists across the globe to monitor the situation and study the new sub-variant, as many have already been doing.

As of last Friday, BA.2 had already been detected in at least 40 countries, including the United States. It has already spread quickly in Denmark, where early reports indicate it doesn't appear to be deadlier than its parent variant. The sub-variant is now also spreading rapidly in the United Kingdom.

While BA.2 is a descendent of omicron, it has slightly different mutations. Omicron has several sub-variants, as does the previously dominant, highly transmissible delta variant.

-ABC News' Sony Salzman

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