image copyrightGetty Imagesimage captionThe Delta variant could make up 90% of cases by late August, experts warn
German Chancellor Angela Merkel has warned Europe is "on thin ice" with the spread of Covid-19's Delta variant.
"Even if the third wave has been broken, the pandemic is not yet over," she told Germany's parliament.
Her warning came as the European Centre for Disease Prevention and Control (ECDC) said the variant would account for 90% of EU cases by late August.
The Delta variant, first identified in India, is thought to be 40%-60% more transmissible.
ECDC director Andrea Ammon said on Wednesday that the spread of the variant showed the importance of speeding up vaccinations in Europe, as "preliminary data shows that it can also infect individuals that have received only one dose of the currently available vaccines".
Two doses offered "high protection" against the Delta (B.1.617.2) variant, she added.
The predominant variant in Europe at the moment remains Alpha (B.1.1.7), which was first discovered in the UK and spread across the continent early this year.
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On Wednesday Mrs Merkel said that, like Germany, all of the EU should quarantine arrivals from the UK considering the dangers of the spread of Delta.
The UK is not on the EU's list of safe countries, due to the spread of Delta, but that list is not binding on member states.
UK Prime Minister Boris Johnson has said that while fully vaccinating people offered "a good way forward" for resuming travel, this summer would not be "like every other. This is going to be a more difficult summer to take a holiday".
Here is how different parts of Europe are dealing with the threat of Delta.
Although cases in France have been falling, Delta is causing concern in an area in the south-west of the country.
On Thursday, Prime Minister Jean Castex and the country's health minister are to visit Les Landes, where the variant accounts for 70% of infections. Across France, it is believed to be behind 10% of cases.
Although most lockdown have been lifted in France, a resurgence in cases could lead to a return to restrictions.
On Thursday, Russia recorded more than 20,000 new cases and 569 deaths – the highest figures since January.
image copyrightEPAimage captionMoscow has seen a spike in cases but vaccination levels remain low in Russia
In the capital Moscow – which has seen its highest number of daily deaths since the pandemic began – the Delta variant is responsible for 90% of new infections, according to the city's mayor.
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The spread of the variant has been complicated by low vaccination uptake across the country.
Although Russia was one of the first countries to develop a vaccine, only 12.8% of Russians had received a single dose and 9.9% were fully vaccinated by 16 June.
Portugal's health minister has admitted the country could have "acted differently" to prevent the spread of the variant, which now accounts for more the half of new cases in Lisbon and the Tagus Valley.
Her comments came after Angela Merkel said the situation in Portugal could have been avoided with EU-wide travel rules, after Portugal allowed travellers from the UK to enter with a negative test.
Separately, the head of Portugal's vaccination programme has said the country may miss its target of providing at least a first dose to 70% of the population by early August if shortages continue.
image copyrightGetty Imagesimage captionDelta now accounts for more than half of new cases in Lisbon, PortugalEuro 2020
The German head of the World Medical Association has urged people not to travel to London for Euro 2020 matches over concerns about the Delta variant.
Ahead of Germany's match against England in London next Tuesday, Frank Ulrich Montgomery said that those travelling to the UK "run the risk of getting infected with the Delta variant".
media captionRos Atkins traces back the story of the Delta variant and how it delayed the UK’s reopening plans
"I consider it irresponsible for even vaccinated people to travel to London in this situation," he told Germany's RND news network.
The stadium at Wembley will allow 60,000 fans to watch the tournament's semi-finals and final. It means the stadium will be at 75% capacity for those games.
Health officials in Denmark, meanwhile, have asked 4,000 fans to get tested after three people who attended last Thursday's Denmark v Belgium match contracted the Delta variant.
All three are thought to have been infected at the game.