European nations are racing to vaccinate their populations against the coronavirus amid fears that the highly transmissible delta variant could spark another COVID wave and overwhelm health systems.

European Commission President Ursula von der Leyen voiced her concern over the variant on Friday during a visit to Lithuania. "We are concerned about the delta variant. We see that the new delta variant is much more transmissible than the other ones, and we see that infection rates are rising and we know that they will be rising," she said.

However, von der Leyen added that the existing vaccines were still effective against the variant. The severity of the infection could be reduced through vaccination and hygiene measures, she said in Vilnius.

"I can only urge everybody who has not taken the opportunity to get vaccinated to do so. It is protecting yourself and protecting your environment."

Variant spreads as travel resumes

The rise in delta variant-related cases coincides with Europe's summer holiday months, as more people travel and attend social gatherings. Many countries have also loosened restrictions, allowing people to ditch certain social distancing norms and take up activities in public places.

However, the risk of infection from the delta variant is "high to very high" for partially or unvaccinated communities, according to the European Center for Disease Control (ECDC), which monitors 30 countries on the continent. The agency estimates that by the end of August, the variant will account for 90% of cases in the EU.

"It is very important to progress with the vaccine rollout at a very high pace,'' the ECDC warned.

WHO calls for 'discipline'

The World Health Organization has also called for caution in the face of the new variant, which makes transmission growth "exponential," it said.

The number of new cases is increasing in countries such as the United Kingdom, Portugal and Russia. Meanwhile, experts have also predicted that the delta variant will become the dominant strain of coronavirus in Germany by August.

"The three conditions for a new wave of excess hospitalizations and deaths before the (fall) are therefore in place: New variants, deficit in vaccine uptake, increased social mixing," said Dr. Hans Kluge, the head of the WHO's Europe office. He added that 63% of people in the 53-country superregion that his office covers have also not yet had their first shot.

"There will be a new wave in the WHO European region unless we remain disciplined," he said.

lc/rc (AP, dpa)