In the past fortnight, a heavily mutated Covid variant has been identified, rapidly labelled a "variant of concern" by the World Health Organization and named Omicron. It was first detected in South Africa and the spread some countries including the UK, Hong Kong and a few others.
It is a rapidly evolving situation. Omicron's genetic profile has raised concerns, but there's a shortage of real-world data that means nobody has the complete picture of what it can do.
It is unclear how big a threat it poses.

At Early Stage
Yet, it is at this early stage, in an absence of definitive facts and when there is a danger of both underreacting and overreacting, that the UK government has to act.
It's like you or me deciding whether to marry someone after the first date. Only the stakes are much higher.
What we know is Omicron has mutations that theoretically help it to spread more quickly and there is mounting evidence of that happening in South Africa.

It also has mutations that theoretically make vaccines less effective and the World Health Organization says there is a higher risk of reinfection than with other variants.
But we don't know how transmissible it is. We don't know whether it is milder or more severe. We don't know what will really happen when it comes up against our significant wall of immunity built up through vaccines, boosters and high levels of Covid this autumn.

The government's response is to test everyone coming in to the UK, isolate all Omicron contacts, ramp up boosting and bring back compulsory face masks in some public places.
Let's be clear - that will not stop more Omicron cases arriving or circulating. It's already arrived. If a virus is good at spreading then eventually it will slip through.
And it has the potential to spread here too. Cases of Covid have been climbing except for a lull over the October half term.

They are averaging at more than 40,000 a day and the R number - the average number of people each infected person passes the virus on to - is just above the crucial threshold of one, which means cases are growing.
The government has been focusing on the pressure on hospitals and pre-Omicron this would have been a key factor in whether to tighten restrictions or go for Plan B. But despite the rise in cases, the numbers needing hospital care for Covid has actually been tumbling due to the success of booster vaccines.
But if the current Delta variant can spread here and Omicron combines faster transmission with some ability to evade immunity, then it too has the potential to circulate.
All the measures can do is buy time, but for what? Science and boosters There are important scientific questions that need answering and top of the list is what happens when Omicron meets high levels of immunity. The answer, for better or worse, will dictate what happens next.

The vaccines that have been used in the UK train the body to attack the spike protein on the virus - specifically the version of spike from the original variant from Wuhan in China.
Our immune system learns to attack several parts of that spike. The antibodies in our blood are like a pit crew descending on a Formula 1 car - each going to their target area. But the mutations in Omicron are like changing some parts of the car to bamboozle the mechanics and make their job harder.
Any dent to immunity is most likely to affect the odds of you catching Covid. What we've seen from the phenomenon of waning immunity is that protection against severe disease and death is more resilient. It will take time to know for sure.

It might sound odd, but booster doses could limit any impact. In theory you can compensate for a less efficient immune defence by simply throwing more antibodies and T-cells at the problem, even if they are imperfect.
More than 17 million people have already had a third dose and the government wants to ramp up boosting. Other countries have cut the gap between the second and third dose from six months to five and we should hear from the government's vaccine advisers soon.

There is also a desire to understand how sick people are getting with Omicron. It is often incorrectly claimed that a virus must become milder as it mutates. The reality is much more complicated and it will take time to get the answer as the country with the most confirmed cases, South Africa, has a relatively young population. The younger you are the milder Covid tends to be.
There are already cries that the government is both over-reacting and not going far enough.

The problem for all of us is we'll only know the right answer with hindsig The latest is the most heavily mutated version discovered so far - and it has such a long list of mutations that it was described by one scientist as "horrific", while another told me it was the worst variant they'd seen.
It is early days and the confirmed cases are still mostly concentrated in one province in South Africa, but there are hints it may have spread further.
Immediately there are questions around how quickly the new variant spreads, its ability to bypass some of the protection given by vaccines and what should be done about it.
There is a lot of speculation, but there are very few clear answers.

What do we know?
The variant has been named Omicron by the World Health Organization, following the pattern of Greek code-names like the Alpha and Delta variants.
It is also incredibly heavily mutated. Prof Tulio de Oliveira, the director of the Centre for Epidemic Response and Innovation in South Africa, said there was an "unusual constellation of mutations" and that it was "very different" to other variants that have circulated.

"This variant did surprise us, it has a big jump on evolution [and] many more mutations that we expected," he said.
In a media briefing Prof de Oliveira said there were 50 mutations overall and more than 30 on the spike protein, which is the target of most vaccines and the key the virus uses to unlock the doorway into our body's cells.
A lot of mutation doesn't automatically mean: bad. It is important to know what those mutations are actually doing.
Prof Richard Lessells, from the University of KwaZulu-Natal in South Africa, said: "They give us concern this virus might have enhanced transmissibility, enhanced ability to spread from person to person, but might also be able to get around parts of the immune system.

There have been many examples of variants that have seemed scary on paper, but came to nothing. The Beta variant was at the top of people's concerns at the beginning of the year because it was the best at escaping the immune system. But in the end it was the faster-spreading Delta that took over the world.

Prof Ravi Gupta, from the University of Cambridge, said: "Beta was all immune escape and nothing else, Delta had infectivity and modest immune escape, this potentially has both to high degrees."
Scientific studies in the laboratory will give a clearer picture, but answers will come more quickly from monitoring the virus in the real world.
It is still early to draw clear conclusions, but there are already signs that are causing worry.

(Courtesy: BBC)