Austria's Chancellor Sebastian Kurz on Friday suggested that some European countries may have signed "secret contracts" with vaccine companies to receive more vaccines than they were entitled to based on EU rules.  

EU members have agreed that vaccines should be distributed among countries based on population size, but Kurz said that after comparing total procurement between member states, it became clear that "deliveries do not follow the per capita quota system".

"There are clues that point to so-called bazaars where additional agreements between member states and pharmaceutical companies were made," Kurz said. 

"Malta will receive three times as many doses per capita as Bulgaria until the end of July," he said. 

"The Netherlands would not only receive more doses of vaccine per capita until the end of June than Germany, but almost twice as many as Croatia," Kurz said.

"This is in clear contradiction to the political goals of the EU," he said. 

But an EU spokesman downplayed the claims of backroom deals. 

"Member states may decide to ask less or more of a given vaccine, and this is discussed between the member states," Stefan de Keersmaecker said. 

"It's possible in this context, following the outcome of the discussions between the member states, that a new distribution key is agreed upon with the company," he said.

The European Union has come under fire for its sluggish vaccine rollout, which it has blamed on supply and delivery problems. 

European nations lag behind the United States, Israel and the United Kingdom in terms of the percentage of the population that has already received at least one dose. 

Malta leads the EU in terms of vaccine rollout, with around 17 per cent of the country's adult population having received at least one vaccine dose so far. As of Thursday, healthcare workers in the country had administered 113,258 vaccine doses.