Meanwhile in Bulgaria, the NOVA television reported on Wednesday evening that the health ministry has accused AstraZeneca of delaying vaccine supplies, which was later confirmed on Thursday by Health Minister Kostadin Angelov at his regular weekly press conference.

Amid the "race against the virus, we were extremely unpleasantly surprised by another non-compliance with the agreement by the company," Angelov said.

By the end of August, Bulgaria booked 4,518,323 doses of the Oxford-AstraZeneca vaccine. The country has received 117,600 doses by Feb. 26. "The quantity was reduced to 40 percent of those expected," Angelov said.

"Within three days we have had serious talks with the supplier company at various levels," he said. "We received only one letter stating that 'the production of vaccines is a process of a high degree of technical complexity' and 'we expect to be able to deliver vaccines to Bulgaria.'"

"We do not need your courtesy. We need vaccines," Angelov added.