A new strain of coronavirus first detected in the UK has prompted dozens of travel bans and widespread concern about what this means for the world.
While scientists dig deeper, here's what this new strain means for you:
Why is this strain important?
The new variant has a series of mutations, the US Centers for Disease Control and Prevention said.
"Based on these mutations, this variant strain has been predicted to potentially be more rapidly transmissible than other circulating strains of SARS-CoV-2" -- the scientific name for the novel coronavirus, the CDC said.
England's Chief Medical Officer Chris Whitty said Saturday the new strain "can spread more quickly" and was responsible for 60% of new infections in London.
On Monday, an epidemiologist from the World Health Organization said, "We are hearing that it could spread up to 70% faster."
"What they're seeing is that the reproduction number -- so this is the number of individuals that an infected person transmits to -- has increased from 1.1 to 1.5," said Maria Van Kerkhove, the WHO's technical lead for Covid-19.
"I just want to put into context this up-to-70% increase."
Van Kerkhove said it's not yet clear whether that increase "is associated with the variant itself," or if it's due to human behavior.
So far, "there is no evidence that this variant causes more severe illness or increased risk of death," the CDC said Tuesday.
But a strain that spreads faster could lead to more infections, which in turn might lead to more hospitalizations and deaths.
Where is this strain now?
Outside the UK, this strain has been detected in countries such as Denmark, Belgium, the Netherlands, Italy and Australia. A similar but separate variant also has been identified in South Africa.
As of Tuesday, the strain "has not been identified through sequencing efforts in the United States, although viruses have only been sequenced from about 51,000 of the 17 million US cases," the CDC said.
"Given the small fraction of US infections that have been sequenced, the variant could already be in the United States without having been detected."
Epidemiologist Dr. Celine Gounder said she thinks this strain is already in the US because it's been circulating in the UK for months before this recent surge.
Public Health England said backward tracing (using genetic evidence) suggests the strain first emerged in England in September. It then circulated in very low levels until mid-November.
"Because this virus has been circulating for some period of time in the UK already, the cat's out of the bag," Gounder said. "It has spread elsewhere, including the United States."
Who's getting infected the most with this strain?
"Most COVID-19 cases from whom this variant has been identified have occurred in people under 60 years of age," the World Health Organization said Tuesday.
That can be problematic because "when people are asymptomatic, they usually are under age 60," CNN Senior Medical Correspondent Elizabeth Cohen said.
"So that may be why this is spreading so quickly -- or part of the reason -- is that many of these people aren't showing symptoms, so they're running around and spreading it."
Of course, people can be contagious for days before they get symptoms. And some young people suffer long-term effects from Covid-19, too.
While severe illness from Covid-19 is relatively rare in children, "there is a hint is that [the new strain] ... has a higher propensity to infect children," said scientist Neil Ferguson, a member of the UK's New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG),
But he said more data is needed.
How do I protect myself from this new strain?
This new strain means "we have to work a little bit harder about preventing the spread," Van Kerkhove said.
Gounder agreed. "What we really need to be doing is focusing on the things we know will prevent spread of this new variant -- which is the same thing that works against spread of the coronavirus in general," she said.
"That is masks, social distancing."
Will vaccines work against this new strain?
Both the Pfizer/BioNTech vaccine and the Moderna vaccine have shown efficacy rates of around 95% in clinical trials. But now many wonder if the vaccines would work on variant strains on the virus -- like the one spreading rapidly in the UK.
Pfizer and Moderna said they're testing their vaccines to see if they work against the UK-based strain.
The new strain could mean more people will need to get vaccinated to achieve herd immunity, BioNTech CEO Ugur Sahin said Tuesday.
"On the topic of herd immunity, there is always the discussion about 60% to 70%," Sahin said.
"But if the virus becomes more efficient in infecting people, we might need even a high vaccination rate to ensure that normal life can continue without interruption."
The novel coronavirus has mutated before, and both vaccines have worked against variations of the virus.
"Up to now, I don't think there has been a single variant that would be resistant to the vaccine," Moncef Slaoui, chief science adviser for Operation Warp Speed, said Sunday.
"We can't exclude it, but it's not there now."
Scientists at the Walter Reed Army Institute of Research are examining the variant and expect to know in the next few days whether vaccines might not work against it.
How does this strain impact travel?
At least 24 countries are now banning passenger travel from the UK, including Canada, Russia, Chile, Italy, Iran and Sweden.
So far there are no plans for the US to enact a travel ban against the UK, US Assistant Secretary for Health Adm. Brett Giroir said Monday.
British Airways, Delta Airlines and Virgin Atlantic have agreed to require passengers get tested for Covid-19 before boarding planes from the UK to New York, Gov. Andrew Cuomo said.
But some health experts say Americans shouldn't be traveling anyway because new Covid-19 hospitalizations and deaths are soaring -- and it's easy to infect loved ones without realizing it.
"This is really not the time to be traveling," Gounder said.