The region has some of Europe's lowest vaccination rates, particularly in Romania and Bulgaria, and saw some of the highest COVID-related death rates towards the end of 2021.

Poland reported 53,420 new COVID-19 cases on Wednesday, while the Czech Republic registered record daily tallies of new coronavirus cases for two days in a row this week, reaching almost 40,000 on Tuesday.

Hungary, a country of 10 million, reached over 20,000 new daily coronavirus cases while the EU's least vaccinated countries, Romania and Bulgaria, also reported record high case counts.

"We have to be ready for a further rise in cases, even above 60,000," a Polish Health Ministry spokesperson told a news conference.

However, countries have yet to set tougher and more sweeping restrictions, such as mandatory lockdowns, unlike during earlier waves of the pandemic in 2020-21 when strict measures were imposed.

The World Health Organization said on Jan. 12 that Omicron causes less serious illness than earlier variants of the coronavirus but that it remained a "dangerous virus", especially for the unvaccinated.

Poland said older primary and secondary schoolchildren must switch to remote learning from Thursday, but restaurants, cinemas and other public places could remain open.

There are some limits on unvaccinated customers in Poland, but enforcement is lax.

In an effort to shield businesses and minimise the extent of remote learning, Bulgaria recently said it would impose tougher restrictions based on occupancy of intensive unit beds, rather than based on number of daily infections.

Poland has stepped up testing, performing a record 173,000 official tests in 24 hours. Yet the number of tests per thousand people in the country of 38 million remains much lower than in Western European countries, Our World in Data shows.

(Reporting by Joanna Plucinska, Pawel Florkiewicz and Anna Wlodarczak-Semczuk in Warsaw, Luiza Ilie in Bucharest, Robert Muller in Prague, Krisztina Than in Budapest, Tsvetelia Tsolova in Sofia; Writing by Joanna Plucinska; Editing by Simon Cameron-Moore, Kevin Liffey and Mark Heinrich)