China has ordered a full quarantine in Shenzhen, a city of 17.5 million people, as it tries to contain the worst COVID-19 outbreak in several provinces in the country, with the number of cases doubling to 3,400 over the past weekend.

Businesses in this financial and technological center of China, which borders Hong Kong, are shutting down or operating remotely unless they supply food, utilities or other basic services.

The restrictions will remain in place until at least March 20, adding Shenzhen to other cities that have imposed various restrictions, including China’s most populous city Shanghai and Changchun in Jilin province in the northeast. Of the 1,938 newly confirmed cases on Sunday, more than 1,400 were in Jilin province.

Europe has also seen a marked increase in the virus in some countries.

In the UK, one in 25 people are infected, according to the latest estimates from the Office for National Statistics (ONS), which reports that a sub-variant of the Omicron strain, called BA.2, is the most common strain in the UK.

According to the U.S. Centers for Disease Control and Prevention (CDC), the BA.2 sub-variant may be 30% more infectious than the original Omicron strain, but this new sub-variant of the virus is now being investigated following an increase in incidence in the country.

In Germany, authorities have also warned against a rise in BA.2, with the country’s public health institute (RKI) reporting that the coronavirus infection rate hit a record high for the third consecutive day on Monday at 1,543 per 100,000 people, continuing a steady rise since early March. The disease outbreak is showing signs of worsening, Bloomberg writes.

COVID-19 infections are also on the rise again in that country, according to France’s public health authority. The number of new infections topped 73,000 on Friday, up 20 percent in recent weeks, according to France 24.

To help fend off the new wave of COVID-19, people will need a fourth dose of the vaccine, as Pfizer CEO Albert Bourla said on Sunday. The pharmaceutical company will continue to work on its vaccine that works against all strains.

On Feb. 22, the World Health Organization (WHO) classified BA.2 as a “strain of concern.”

On March 8, the agency warned that “Omicron consists of several genetically related sublines, including BA.1, BA.2, and BA.3, each under surveillance by WHO and its partners. Globally, BA.1 has been the predominant omicron lineage, but in recent weeks the proportion of reported sequences of BA.2, has increased compared to BA.1, and it is the predominant omicron variant in several countries. “BA.1 and BA.2 have some genetic differences that may make them distinct in atigenes.”