In its latest threat assessment report, the ECDC said on Wednesday that since the Delta variant is 40-60 per cent more transmissible, it is projected to cause 70 per cent of the new infections in the European Union (EU) and the European Economic Area (EEA) by early August.
By late August, this figure could reach 90 per cent, Xinhua news agency reported citing the Centre as saying.
The ECDC also warned that the daily number of new cases, hospitalisations and deaths, could increase to the late 2020 levels if non-pharmaceutical measures, such as physical distancing, hand and respiratory hygiene, use of face masks, are relaxed.
The ECDC said the Covid-19 vaccination campaigns must be accelerated and the second doses should also be administered as early as possible.
"Unfortunately, preliminary data shows that (the Delta strain) can also infect individuals who have received only one dose of the currently available vaccines," ECDC Director Andrea Ammon said.
"It is very likely that the Delta variant will circulate extensively during the summer, particularly among younger individuals who are not targeted for vaccination. This could cause a risk for the more vulnerable individuals to be infected.
"They could experience severe illness and death if they are not fully vaccinated," she said.
Nevertheless, Ammon stressed that there is still hope.
"The good news is that having received two doses of any of the currently available vaccines provides high protection against this variant and its consequences.
"However, about 30 per cent of individuals older than 80 years and about 40 per cent of individuals older than 60 years have not yet received a full vaccination course in the European Union," she added.