The notion of coronavirus immunity is still in question after an announcement from South Korea's CDC.

In a Monday briefing, South Korea's Centers for Disease Control and Prevention announced 51 people "cured" after contracting COVID-19 had tested positive for the disease after being released from quarantine. CDC Director Jeong Eun-kyeong leaned toward deeming these cases a "reactivation" of the virus, but will study it further.

While it was never certain, the idea that people who test positive for and then recover from the new coronavirus gain immunity from the disease had even informed government policy in some countries. The U.K. originally resisted closing down businesses and enforcing social distancing guidelines in an effort to spread "herd immunity" among its citizens, for one.

But this latest announcement calls the herd immunity strategy into further question. Patients are deemed recovered when they test negative for the disease twice in 24 hours. Yet in at least 51 cases, people who had apparently recovered had tested positive again shortly after they left quarantine. "While we are putting more weight on reactivation as the possible cause, we are conducting a comprehensive study on this," Jeong said. Those patients may not have even been cured at all, seeing as "there have been many cases when a patient during treatment will test negative one day and positive another," he said. Kathryn Krawczyk

The new Biden administration has yet not disclosed the secrets of Area 51 or explained what the Air Force really knows about UFOs, but it did clarify, at least, the mystery of the vanished "Diet Coke button" former President Donald Trump would use to summon refreshments in the Oval Office. The usher button, as it is formally known, is not gone, even if it is no longer used to summon Diet Cokes, a White House official tells Politico.

The White House official "unfortunately wouldn't say what Biden will use the button for," Politico's Daniel Lippman writes, suggesting Biden might summon Orange Gatorade and not the obvious answer, ice cream — or, let's get real, coffee. What's more, there are evidently two usher buttons in the Oval Office, one at the Resolute Desk and the other next to the chair by the fireplace, a former White House official told Politico, adding that Trump didn't actually use the Diet Coke button all that much because "he would usually just verbally ask the valets, who were around all day, for what he needed."

In any case, it is not the placement of the button that matters, of course, but how you use it. And Biden will presumably know better than to order ice cream treats during a top-secret national security briefing. Peter Weber

At 6 p.m. on the dot, they start to appear on their front lawns, ready to belt out everything from "God Bless America" to "Baby Shark."

In this Minneapolis neighborhood, residents have been participating in nightly singalongs since the beginning of the pandemic. Each family is a safe distance apart, as no one leaves their yard. They have a 200-song repertoire, and neighbor David O'Fallon told the Star Tribune they gather "rain, shine, or meteor shower."

About 20 people — ranging in age from 2 to 80-something — usually join the chorus. Over the last 300 or so nights, they have become closer, despite the physical distance. "We know each other better now," O'Fallon said. "We are stronger as a small community. We lift each other's spirit." Catherine Garcia

For the third night in a row, riots broke out in the Netherlands on Monday as people angry over a new COVID-19 curfew clashed with police.

For the first time since World War II, the Netherlands has a curfew in place, from 9 p.m.to 4:30 a.m.; violators face a $115 fine. In The Hague on Monday night, groups of men threw rocks and fireworks at police officers, with some also setting fires, BBC News reports. In Rotterdam, after the crowd did not disperse, law enforcement fired warning shots and tear gas. More than 150 people were arrested across the country in connection with the riots.

The situation was worse on Sunday, when more than 250 people were arrested; Dutch police said they witnessed the worst unrest they've seen in 40 years. Prime Minister Mark Rutte condemned the rioting, saying it is "unacceptable. All normal people will regard this with horror. What motivated these people has nothing to do with protesting, it's criminal violence and we will treat it as such."

To try to combat the coronavirus pandemic, bars and restaurants have been shuttered in the Netherlands since October, and non-essential stores and schools closed in December. The country has reported almost 1 million COVID-19 cases and more than 13,500 deaths, according to the Johns Hopkins University coronavirus database. Catherine Garcia

At least one person was killed and five more injured in Portland, Oregon, on Monday afternoon as an unidentified driver went on a hit-and-run spree, steering his silver Honda Element on sidewalks and over laws as he apparently targeted pedestrians along a 15-block stretch in the Southeast quadrant of the city. After the man crashed into an El Camino, neighbors and bystanders prevented him from escaping by foot until police arrived and took him into custody.

Videos of the arrest show the man, who appears to be white and middle-aged, in a standoff with bystanders before police arrived and struggled to put him in cuffs. Several witnesses told The Oregonian the car had Washington plates. Police have not released the name of the driver or any of his victims.

Larry Wolfe told The Oregonian he had an appointment to meet the person killed, a woman in her 70s, and he saw the car hit the woman, turn around and hit her again, then do a U-turn and drag her down the street. Another witness, Arun Gupta, gave a similar account to OPB. "She was struck once, knocked up on the sidewalk ... and then the car did a U-turn, came up on the sidewalk, struck her and dragged her down to Stark and 19th," he said.

Other witnesses described a chaotic scene where the driver, speeding and running red lights, hit cyclists, struck several pedestrians, and pinned two people between and SUV and a retaining wall. Read more witness accounts at The Oregonian. Peter Weber

President Biden is expected to announce several executive actions on Wednesday meant to fight climate change, including one asking government agencies to determine the extent of a drilling ban on federal land, two people with knowledge of the matter told The New York Times on Monday.

Additionally, Biden intends to direct the government to conserve 30 percent of all federal land and water by 2030, make climate change a national security priority, and form a task force to create an action plan on ways to reduce greenhouse gas emissions, the Times reports. He will also create multiple commissions to focus on environmental justice and green jobs, specifically helping minority communities and people who live in coal country.

Environmentalists say to really curb harmful emissions, Biden will have to enact legislation; otherwise, he will need to rely heavily on the regulatory process. "The climate reality of today is higher temperatures, stronger storms, more destructive wildfires, sea-level rise, acidifying oceans, and extended drought," Sherri Goodman, senior fellow at the Wilson Center's Environmental Change and Security Program, told the Times. "We need a climate security plan for America that climate-proofs American infrastructure and puts climate and clean energy innovation front and center." Catherine Garcia

In an interview with MSNBC's Rachel Maddow on Monday afternoon, Senate Majority Leader Chuck Schumer (D-N.Y.) said his caucus won't allow Minority Leader Mitch McConnell (R-Ky.) to dictate the agenda in the Democratic-led 50-50 Senate or demand an end to the legislative filibuster as a precondition for a power-sharing pact. "We've told McConnell no on the organizing resolution, and that's that. So there's no negotiations on that," Schumer said, suggesting he had a secret plan. "There are ways to deal with him."

Maddow included an update when she broadcast the interview Monday night. "While we were airing that right now, and you were watching it, Republican Minority Leader Mitch McConnell just put out a statement that he is folding on this" and willl "agree to go forward with what Sen. Schumer told him he must," she said. "Sen. Mitch McConnell has caved and Sen. Schumer has won that fight. That was quick. Let's see what else we can do."

McConnell said he would allow the Senate to move forward because two Democrats had reiterated their opposition to ending the filibuster, effectively taking that option off the table. Maddow asked Schumer about that, too, and he didn't answer directly.

"The caucus is united with the belief that I have: We must get big, strong, bold things done," Schumer said. The Democratic caucus is also "totally united" that "we will not let Mitch McConnell dictate to us what we will do and not do," and "we have tools that we can use," notably the budget reconciliation process," he added. "We will come together as a caucus and figure it out."

Schumer also suggested he is not interested in playing cat-and-mouse with McConnell's Republicans again. Watch below. Peter Weber