A new variant of coronavirus has been blamed for the introduction of strict tier four mixing rules for millions of people, harsher restrictions on mixing at Christmas in the UK, and other countries placing the UK on a travel ban.

Specialists have “moderate” confidence that the new variant is more able to transmit than other variants.

All the work is at an early stage, contains huge uncertainties and a long list of unanswered questions.

Three things are coming together that mean it is attracting attention:

• It is rapidly replacing other versions of the virus
• It has mutations that affect part of the virus likely to be important
• Some of those mutations have already been shown in the lab to increase the ability of the virus to infect cells

All of these come together to build a case for a virus that can spread more easily.

However, we do not have absolute certainty. New strains can become more common simply by being in the right place at the right time – such as London, which had only tier two restrictions until recently.

But already the justification for tier four restrictions is in part to reduce the spread of the variant.

The variant was first detected in September. In November around a quarter of cases in London were the new variant. This reached nearly two-thirds of cases in mid-December.

The virus that was first detected in Wuhan, China, is not the same one you will find in most corners of the world.

The D614G mutation emerged in Europe in February and became the globally dominant form of the virus.

Another, called A222V, spread across Europe and was linked to people’s summer holidays in Spain.

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An initial analysis of the new variant has been published and identifies 17 potentially important alterations.

There have been changes to the spike protein – this is the key the virus uses to unlock the doorway to our body’s cells.

One mutation called N501Y alters the most important part of the spike, known as the “receptor-binding domain”.

This is where the spike makes first contact with the surface of our body’s cells. Any changes that make it easier for the virus to get inside are likely to give it an edge.

The other mutation – a H69/V70 deletion, in which a small part of the spike is removed – has emerged several times before, including famously in infected mink.

Work by Prof Ravi Gupta at the University of Cambridge has suggested this mutation increases infectivity two-fold in lab experiments.

Studies by the same group suggest the deletion makes antibodies from the blood of survivors less effective at attacking the virus.

The variant is unusually highly mutated.

The most likely explanation is the variant has emerged in a patient with a weakened immune system that was unable to beat the virus.

Instead their body became a breeding ground for the virus to mutate.

There is no evidence to suggest that the infection is more deadly, although this will need to be monitored.

However, just increasing transmission would be enough to cause problems for hospitals.

If the new variant means more people are infected more quickly, that would in turn lead to more people needing hospital treatment.

It appears that all three leading vaccines develop an immune response against the existing spike, which is why the question comes up.

Vaccines train the immune system to attack several different parts of the virus, so even though part of the spike has mutated, the vaccines should still work.

Vaccine escape happens when the virus changes so it dodges the full effect of the vaccine and continues to infect people.

This may be the most concerning element of what is happening with the virus.

This variant is just the latest to show the virus is continuing to adapt as it infects more and more of us.