The Omicron variant is now dominant in the US

Omicron will lead to a spike in cases in the upcoming weeks, but those who are vaccinated and unvaccinated will have a “stark difference” in experience, US Surgeon General Dr. Vivek Murthy told anchor Tony Dokoupil on “CBS Mornings” Monday.

For people who have maximum protection from vaccines and boosters, Murthy said that they either won’t get an infection, or if they do, it will most likely be mild.

“If you are unvaccinated, I’m worried about you. I’m worried that your risk of being hospitalized, or God forbid, losing your life to this virus, is quite significant,” Murthy said. “It still remains the case that getting vaccinated and boosted is the best way to protect yourself, even against Omicron.”

Biotechnology company Moderna continues to work on developing Covid-19 boosters that specifically target certain variants, including Delta and Omicron, Dr. Stephen Hoge, president of the company, said Monday.

For now, Moderna plans to focus its "immediate efforts" around Omicron on advancing the current vaccine that is already available, Hoge said.

Moderna's current coronavirus vaccine booster is authorized for emergency use in the United States and administered as a half-dose at 50 micrograms.

Moderna announced Monday that preliminary data suggests its half-dose booster shot increased antibody levels 37-fold against Omicron compared with the levels seen when a fully vaccinated person does not receive a booster – but a larger-sized dose of the booster, at 100 micrograms, increases antibody levels 83-fold.

Earlier on Monday, Dr. Angelique Coetzee, national chair of the South African Medical Association, said Covid-19 case numbers in the country have started to decline. However, the United States and South Africa have key differences, which create "issues with extrapolation" on how the Omicron variant may behave in the two countries, according to Dr. Leana Wen.

"It looks like they were looking at a trajectory of three to four weeks of Omicron really being dominant and driving the number of infections, and now it's trending down again. In the US, there are some issues with extrapolation," Wen explained.

Omicron may take time to get to some parts of the US.

"We have a lot of different parts of the country, including some that are not well-vaccinated. Other parts where it might take a little bit of time for Omicron to get to. So I don't think we could say that the US as a whole will be out of this in three to four weeks. It might be a case of rolling cases, where there are large numbers of infection in parts of the country that then cycle to others," Wen said.

The population makeup is different.

"South Africa has a much younger population. The individuals also who were initially infected tended to be young people. So even if they were unvaccinated, the chance of them becoming severely ill is relatively low. Here in the US, we have not yet seen what happens when Omicron rips through nursing homes, as an example," Wen added.

Covid-19 case numbers in South Africa have started to decline, said Dr. Angelique Coetzee, national chair of the South African Medical Association, on Monday.

“What we currently see is our cases, sort of, we’re over the curve – it’s sort of coming down. You know, in Gauteng, which was the epicenter, the numbers are much lower,” Coetzee told CNN.

While she did note that Covid-19 is still spreading in other areas of the country because of the holidays, "in total, if you look at our numbers, it’s going down."

The positivity rate is still high at around 30%, she added.

The Omicron variant has not caused the death rate to spike and the cases are "much, much" less severe than Delta cases, and the Coetzee said.

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The UK government will hold a Cabinet meeting chaired by Prime Minister Boris Johnson at 2 p.m. local time (9 a.m. ET) to provide an update on the latest Covid-19 situation, his office said Monday.

The meeting comes amid speculation that further restrictions or a lockdown is being considered over the Christmas period due to a surge in cases, and warnings from government scientists that hospitalizations could reach 3,000 per day in England.

"At this point, we're still monitoring the data and keeping a very close eye on it," the PM’s official spokesman said Monday, according to the PA Media news agency. "We'd update if any further decisions are taken."

Rafael Nadal has tested positive for Covid-19 after arriving back in Spain from Abu Dhabi, he announced on Monday.

Spain's 20-time tennis Grand Slam champion made his comeback from injury in the Mubadala World Tennis Championship exhibition event in Abu Dhabi last week. 

It was Nadal’s first tournament appearance since the Citi Open in Washington in August.

In a Twitter thread, the 35-year-old said he had tested positive for the virus following a PCR test taken on arrival back in Spain, but did not confirm the specific variant of Covid-19 he had contracted.

Nadal added that he had tested negative at all times when he was in Kuwait and Abu Dhabi and had last tested negative on Friday.

“I am experiencing some unpleasant moments but I hope that I will improve little by little. I am now confined at home and have informed those people who have been in contact with me of the result,” he wrote.

"As a result of the situation I have to have complete flexibility with my calendar and will be analysing my options depending on my progress. I will keep you informed of any decision about my future tournaments," Nadal added.

With Covid-19 cases spiking around the world right before Christmas, many are trying to decide if they should still go ahead with their plans to gather and celebrate with family.

Dr. Leana Wen, CNN medical analyst and former Baltimore City health commissioner, recommends some safety precautions for those who want to keep their Christmas plans.

Quarantine for at least three days before your visit.

If a person is vaccinated, "ideally they leave three days in between, essentially they quarantine in that period, and get tested again" before visiting an older and/or immunocompromised person.

"We know that breakthrough infections are happening. It doesn't mean the vaccines don't work. It means there is so much virus around us, even vaccinated people are getting the spillover effect," Wen said Monday.

Get tested.

"If somebody who is vaccinated visits unvaccinated family members, ideally everybody should get tested on the day of the visit," she explained.

Observe the "two out of three" rule.

For people who are gathering indoors over the holidays, Dr. Wen recommends that you have two out of the three things — vaccination, testing or masking.

"The closer your test is to when you're gathering with people the better," she added.

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The annual World Economic Forum (WEF) in Davos, due to take place in January, has been deferred due to “continued uncertainty” over the Omicron outbreak.

“Current pandemic conditions make it extremely difficult to deliver a global in-person meeting," said WEF in a statement.

WEF plans to reschedule the event for summer 2022, with some digital events to be held in January.

It will be the second year in a row that an in-person event has not taken place. Davos was canceled in 2021 and moved online due to the Covid-19 outbreak.

Israel's daily Covid caseload has risen above 1,000 for the first time in two months as the country’s fifth wave of Covid-19 infections begins to take hold.

There were 1,004 new infections recorded on Sunday, according to the Health Ministry, and the country’s R number -- the number of people infected by each Covid sufferer -- jumped to 1.22, its highest level since August. 

Earlier in the day, the office of Prime Minister Naftali Bennett said government ministers had approved adding the US, Canada and eight other countries to its “red” no-fly list. Israelis will be banned from flying to these countries from Wednesday unless they have special permission. 

Travelers returning from countries on the list will have to self-isolate for 7 days.

At first, they will have to stay in a designated “quarantine hotel,” before being allowed to return home as long as they return a negative PCR test result and agree to have their movements tracked. 

Israel has been steadily adding countries to its red list, including the UK and Italy. Many African countries are also on it. Most of Israel’s 175 confirmed cases, and 380 suspected ones, recently returned from overseas. 

On Sunday evening, Bennett held a televised news conference imploring Israelis to take the new wave seriously, and encouraging those employed in the private sector to work from home. Public sector workers are expected to follow suit next week. 

He also sought to reinvigorate Israel’s stalling vaccination campaign, especially among children, where takeup has been especially weak. 

“The time we bought is running out,” said Bennett, but “with God’s help we will safely overcome this wave."