Recent uptake of COVID-19 vaccine booster doses in the European Union has been "rather disappointing," an official said on Thursday, amid concerns that protection against severe cases of the disease could weaken during the winter.

The European average rate of re-vaccination, or receiving booster doses, was only 29% in the groups of people considered to be at highest risk, such as the elderly and immunocompromised people.

"It is of concern that those most at risk of hospitalisation or severe COVID are not adequately protected," the European Medicines Agency's head of health threats and vaccines strategy, Marco Cavaleri, told a news briefing.

Though there have not been major increases in COVID-19 case rates in recent weeks, Cavaleri said that could change during the colder winter months.

WHO data released late on Wednesday showed that 724,000 new COVID-19 cases were reported in the EU over the past week, down 11% from the previous week. In early October, when experts were warning of a new COVID-19 wave, the number of weekly cases reached 1.5 million.

"This virus is maintaining a fast pace in its evolution, and new subvariants of Omicron and its offspring are on the rise," Cavaleri said, adding that these are more resistent to vaccines.

(Reporting by Ludwig Burger in Frankfurt and Maggie Fick in London Editing by Alex Richardson and David Goodman)