Dozens of countries have banned travel from the UK in an effort to contain a new Covid-19 variant first reported in England.

In a statement on Saturday, the Japanese foreign ministry said the country will ban foreign nationals from entering the country starting Monday through the end of January after several cases of Covid-19 variant were recorded in the country.

The new mutation is being called VUI-202012/01 — the first “Variant Under Investigation” in the UK in December 2020. While scientists hunt for more information about the variant, its impact is already being felt, with dozens of countries imposing restrictions on travelers from the UK.

Here’s what we know so far about the Covid-19 variant:

What is a variant and why are officials concerned about this one? A variant occurs when the genetic structure of a virus changes. All viruses mutate over time and new variants are common, including for the novel coronavirus.

Like other variants, this one carries a genetic fingerprint that makes it easy to track, and it happens to be one that is now widespread in southeast England. That alone does not necessarily mean a variant is more contagious or dangerous.

But scientists advising the UK government have estimated that this variant could be up to 70% more effective at spreading than others. Peter Horby, chair of the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG), said Monday that experts “now have high confidence that this variant does have a transmission advantage” over other variants.

The World Health Organization said Tuesday that the changes to the variant include 14 key mutations, and that some of them “may influence the transmissibility of the virus in humans,” though it added that further laboratory investigations were needed.

Where did the variant originate and how has it taken hold? The new variant is believed to have originated in southeast England, according to the WHO. Public Health England (PHE) says backwards tracing, using genetic evidence, suggests the variant first emerged in England in September. It then circulated in very low levels until mid-November.

Chris Whitty, England’s chief medical officer, said Saturday the variant was responsible for 60% of new infections in London, which have nearly doubled in the last week alone.

Multiple experts have also suggested that this new variant could have been amplified because of a superspreader event, meaning the current spike in cases could also have been caused by human behavior.

Is the new variant more deadly? There is no evidence as of now to suggest that the new variant is more deadly, according to Whitty and the WHO, though it is too early to tell.

Several experts have noted that in some cases, virus mutations that increase transmissibility are accompanied by a drop in virulence and mortality rates.

“As viruses are transmitted, those that allow for increased virological ‘success’ can be selected for, which changes the properties of the virus over time. This typically leads to more transmission and less virulence,” Martin Hibberd, professor of emerging infectious disease at the London School of Hygiene & Tropical Medicine, told the SMC.

Learn more about the UK coronavirus variant here.