The Delta variant is expected to become the dominant Covid strain in Germany within months, denting the country's optimism as it records its lowest infection rates in months.
Lothar Wieler, the head of the Robert Koch public health institute, said the spread of the variant could put unvaccinated people at risk.
“It is really not a question of whether Delta becomes the leading variant, but only when,” Mr Wieler said. “It will have the upper hand in the autumn at the latest.”
Believed to be more transmissible than other strains, the variant first identified in India is spreading rapidly in Britain and has knocked the UK's exit from lockdown off course.
In Germany, it now accounts for about 6.2 per cent of new cases, up from 3.7 per cent at the end of May.
Health Minister Jens Spahn said the variant had the potential to “call into question the successes in fighting the pandemic”.
“The Delta variant is also spreading in Germany – at a low level, but quickly,” Mr Spahn said. “The challenge is that it’s particularly contagious.”
Germany has lifted most restrictions on public life since the third wave subsided and cases dropped to low levels.
Economy Minister Peter Altmaier voiced optimism over Germany’s economic prospects on Friday and said that output would return to pre-pandemic levels by next year.
“The economy is starting up again more quickly than many feared,” he said.
Germany on Friday lifted travel warnings on France, Greece and Spain. But concerns over the Delta variant mean that travel from the UK has been restricted since May 23.
Chancellor Angela Merkel’s chief of staff is advising football fans against travelling to London for the latter stages of Euro 2020.
Helge Braun told German media: “We must remain cautious until everyone has been offered a vaccination”.
Studies in the UK suggest that vaccines are effective at preventing serious disease from the Delta variant but that two doses are essential to achieve this.
About 29 per cent of Germans have had both doses. Germany reached the milestone on Friday of giving a first dose to more than half of its population.
Germany this month opened up vaccinations to all adults and children as young as 12 after the Pfizer/BioNTech shot was approved for younger teenagers.
Mr Spahn said the programme would not be affected by disappointing trial results for a vaccine developed by German company CureVac.
The vaccine proved only 47 per cent effective in an initial trial, a far lower figure than those attained by competitors such as Pfizer and Moderna.
“The results are sobering,” said CureVac’s chief executive Franz-Werner Haas.
“We recognise that demonstrating high efficacy against this unprecedented broad diversity of variants is quite challenging.”
The German government invested about €300 million ($358m) in CureVac last year.
After a slow start, Germany is now administering more than 800,000 shots per day.
“These figures give us confidence,” Mr Spahn said of the vaccine progress.
“Within a few weeks, it will be possible – as things stand, with the deliveries we can expect – to offer vaccinations to all adults who are willing.”