The emergence of the new Omicron Covid variant has sparked concern worldwide due to the high number of mutations it has compared with other variants we've seen so far.
In the UK, face masks and travel testing rules have been tightened up or reintroduced, and vaccine boosters are due to be offered to all over 18's, with a shorter three month gap between second and third doses.
The reason this variant is attracting so much attention is that the number of mutations could have an impact on how the Omicron variant responds to vaccines, how easily transmissible it is, and whether it causes more severe illness.
There's still plenty we don't know, but it's increasingly clear it's very transmissible and it's spreading extremely rapidly in the UK. Work is still underway to understand more about Omicron and to try and limit the spread while scientists look into it further.
For now, it's important to maintain or step up measures to keep yourself and others as safe as possible, and be aware of changing rules.
We round up the key things you need to know below.
This doesn't apply to hospitality settings in England and Wales, but it does in Scotland and Northern Ireland.
The government is also advising face masks should be worn in communal areas of England's schools and colleges. Wales, Scotland and Northern Ireland are urging pupils to wear them in classes as well.
In England from Wednesday 15 December, an NHS Covid Pass (proving your vaccine status) or proof of negative lateral flow test will be required to gain entry to 'nightclubs and settings where large crowds gather - including unseated indoor events with 500 or more attendees, unseated outdoor events with 4,000 or more attendees and any event with 10,000 or more attendees.'
A similar scheme is already in place across the rest of the UK.
In Wales, an NHS Covid Pass showing vaccine status or test results is required for entry into public venues including restaurants, cinemas, and concert halls.
In Scotland and Northern Ireland, proof of vaccine status or negative test result via the Covid Pass is also currently needed for entry into nightclubs and large events.
Across the UK, people are being encouraged to work from home wherever possible.
All contacts of suspected Omicron cases must self-isolate, regardless of their vaccination status. You will be contacted by Test and Trace if this is the case.
All international arrivals to the UK must take a day 2 rapid LFT or PCR test.
Another change to travel rules is that the red list is back: international arrivals from countries on the list - which currently includes 10 countries in the southern part of Africa - will need to pay for hotel quarantine in the UK.
Some countries have tightened restrictions for people travelling from the UK, as case numbers explode here, so keep an eye on changing travel rules.
We don't know yet how well Omicron responds to vaccines, but there is concern that the mutations could help it evade vaccine immunity to an extent.
Experts from the Joint Committee on Vaccination and Immunisation (JCVI) are hypothesising that the vaccines we currently have may be slightly less effective against the new variant - as with the Delta variant - but that they are still likely to be the best way to protect against serious illness, especially with a booster dose.
Information about how the logistics will work to accommodate the millions more people now eligible for a booster shot is expected to be confirmed in stages - many vaccine centres won't yet be set up to process newly eligible groups and progress may vary by area.
People are being encouraged to wait until the NHS says it's their turn to book a booster. The target for offering all over-18's a booster jab is now set for the end of December.
Priority will still be given to older adults and those more at risk of getting seriously ill from Covid.
Pregnant women who have not yet had their vaccine are being urged to get it as the latest data reinforces that it is safe for this group, and that pregnant women are more at risk of getting severely ill from Covid. See the .
There have been some reports of housebound and extremely clinically vulnerable people struggling to access their booster jabs.
Professor Martin Marshall, Chair of the Royal College of GPs, said that while hundreds of thousands of housebound people have had their booster, there are logistical difficulties involved.
He said that getting to people's houses to vaccinate them in-situ is more difficult than vaccinating at centres, particularly with the vaccines that need to be prepared, stored and transported in specific ways, but GP-led teams will be working hard to do this in the most efficient way possible to ensure as many housebound patients are protected as soon as possible.
Whether Omicron or another variant (as Delta is still running high too, resulting in a pandemic double-whammy), it's important to remain vigilant about preventing the spread of Covid, especially with increased indoor mixing, other winter bugs flying around, and the pressure on NHS services.
Here are some of the key ways you can continue to protect yourself and others from Covid:
People who are unvaccinated are much more likely to end up severely ill or hospitalised if they become infected with Covid, and this risk increases with age.
With the much higher transmission rate of Omicron, it's even more vital. We will be better protected collectively if more people have been given a booster dose.
Regular testing with lateral flow tests should help on a population level to detect asymptomatic or pre-symptomatic cases in people and help slow the spread of the virus.
You can . These are for people who do not have symptoms, and usually come in packs of seven. If there aren't any test packs available for delivery at the time you look, you can try booking a collection from a local pharmacy, through the same online service.
Be sure to read the instructions carefully, as they can differ slightly by test pack.
If in doubt, or if you are attending a larger indoor event or socialising, it's sensible to test yourself ahead of time.
Make a fresh commitment to take your mask with you when you're out and about, as they are now mandatory in most shops and on public transport again across the UK.
It's also worth considering an upgrade, especially if you're still relying on masks you bought early on in the pandemic.
Reusable cloth masks will wear out over time, especially with repeated washing and drying, and may not fit as well either if they've shrunk a little.
If you're wondering, with the emergence of the new variant, if it's worth considering a disposable mask instead, take a look at our , which runs through the options and how to decide, and read up on .
Even though we now know that Covid spreads primarily through the air, hand hygiene is still vitally important to protect against seasonal illnesses like cold and flu, and can still be a transmission route.
This is particularly important at the moment because if you get flu and Covid at the same time, you're more likely to be very unwell.
People who are at higher risk from Covid are also at greater risk of complications from the flu, and if more people are ill from flu during the winter, pressure on the NHS will be greater.
It might not be the most appealing prospect as the chill sets in and some areas of the UK are battered with snowstorms (and increasingly high energy bills), but meeting outside where possible, or keeping fresh air flowing when socialising indoors - with open windows, can make a big difference.
The government has been urging people to recognise the importance of ventilation in stopping the spread of Covid. A new campaign this month is encouraging people to open a window every 10 minutes when socialising indoors, to get some air flowing into the room.
You could also meet friends outdoors for a walk, or stock up on thermals and brave outdoor dining.
Story originally published on 30 November 2021, but updated to reflect changing guidance and information.