With record numbers of daily infections in recent days, the UK is currently a hotspot for Omicron - but the latest COVID-19 variant has hit other countries around the world, too.
The US government's chief medical officer Dr Anthony Fauci has called on Americans to get vaccinated, as densely populated areas such as New York City have seen a surge in cases, and some European countries have reintroduced stricter restrictions.
According to data from the World Health Organization (WHO), the UK has reported the highest number of COVID-19 cases in Europe - 436,870 - in the last seven days.
Here's what the COVID situation looks like around the world.
The first Omicron case was detected in the US on 1 December and since then numbers have increased by 40%.
Several large events have been cancelled or postponed, with three NFL matches delayed after outbreaks. The National Hockey League was also forces to cancel games, while performances of the Michael Jackson musical on Broadway have been called off.
Dr Tom Frieden, the former chief of the Centers of Disease Control and Prevention, has urged people to get their booster jabs, warning of a "tidal wave of Omicron likely coming to a hospital near you soon".
Despite the surge in cases, lockdowns of workplaces and social gatherings have not been put in place.
According to WHO data, the US has seen almost 800,000 COVID-related deaths since the pandemic began.
In the past seven days, some 571,461 cases were reported, bringing the total number of coronavirus cases to almost 50 million.
Germany is among several European countries that have introduced tougher measures for UK travellers.
As of midnight on Monday 20 December, people travelling from the UK to Germany have to quarantine.
"The spread of Omicron in the UK is very evident... We have to prevent the spread for as long as possible and slow it down as much as possible," German ministers said in a statement.
People arriving from the UK must also provide a negative coronavirus test under the new rules.
Germany recorded its first Omicron case on 27 November. A total of 297,855 COVID cases have been recorded in the last week.
British tourists can only enter Spain if they show proof of a COVID-19 vaccination.
Until recently, unvaccinated travellers were allowed into the country if they could present a negative PCR test taken 72 hours before their arrival.
"The appearance of new variants... obliges an increase in restrictions," the government has said.
Spain's Industry, Trade and Tourism department said approximately 300,000 British people who are resident in Spain will not be affected by the new measures.
In football, Real Madrid's unbeaten record in La Liga ended on Sunday with a 0-0 draw against strugglers Cadiz - the team had been without six players due to a COVID-19 outbreak at the club.
According to WHO data, some 143,400 cases and 195 deaths have been reported in Spain in the last seven days.
On 16 December, France banned British tourists because of the rise in Omicron cases in the UK.
Those with a "compelling reason" are still able to travel, but have to register the address of their stay in France.
Government spokesman Gabriel Attal told BFM television that restriction measures include reducing the validity of pre-departure PCR tests to 24 hours from 48 for travellers arriving from Britain.
The Delta variant remains dominant in France, which has recorded 350,382 total coronavirus cases and 973 deaths in the past seven days.
Officials in Portugal have not introduced any new COVID-19 measures yet, despite the rise of Omicron.
Almost 30,000 total cases and 107 deaths were reported in the country in the last week.
On 28 November, Dutch health officials detected 13 Omicron cases among people who flew from South Africa - making the Netherlands the first European country to report cases of the new variant.
The country entered into a tough lockdown to curb the spread of Omicron on Sunday 19 December, with non-essential shops, bars, restaurants and other public places closing, as well as schools.
The "unavoidable" lockdown will run until at least 14 January, Prime Minister Mark Rutte has said.
Shops, bars, and restaurants in the country had already been under a 5pm to 5am curfew, which was introduced at the end of November.
A total of 108,521 COVID-19 cases and 391 deaths have been reported in the Netherlands in the past week.
From 6 December, unvaccinated Italians faced tougher rules.
The "super green pass" requires vaccination, rather than including those who have received a recent negative test result. It is compulsory for entry to sports events, concerts, theatres, indoor restaurants and public events.
The previously introduced "green pass", which can be obtained with a negative test result, will be acceptable for the use of local transport and hotels.
In the past seven days, Italy has recorded some 143,400 cases and 750 deaths.