The new contract would include 100 million doses, as well as an option for as many as 200 million more, said the people, who asked not to be identified because the talks are private.

Governments across the EU face growing questions over the slow pace of their vaccine rollouts, and shots from other drugmakers such as AstraZeneca Plc won’t be available for weeks at the earliest.

The attempt to secure more of the Pfizer-BioNTech vaccine comes less than a week after the 27-member bloc boosted its original 200 million-dose order to 300 million. If the option in the new agreement were exercised, it would lift the total doses to 600 million, enough to vaccinate two-thirds of the bloc’s population based on a two-dose regimen.

In premarket trading, BioNTech American depositary receipts rose 2%, with Pfizer showing little change.

Vaccine Rollout

Member countries have pressured the EU to secure more doses as the pandemic’s death toll rises, lockdowns lengthen and leaders worry about containing a new, more contagious strain of the virus that has emerged in the U.K.

While the EU has signed deals with a range of companies for access to almost 2 billion doses, only the Pfizer-BioNTech shot has thus far won approval from its regulator. A decision on a similar vaccine from U.S. biotech Moderna Inc. could come on Wednesday. However, the EU has locked up less of that shot, with a contract for as many as 160 million doses.

“We are in talks about whether and how we can provide further vaccine doses from Europe for Europe this year,” BioNTech Chief Executive Officer Ugur Sahin said in an e-mailed statement.

No agreement has been reached and the numbers could still change. A Pfizer spokesman declined to comment. A BioNTech spokeswoman declined to comment on the number of doses involved.

The European Commission is examining with BioNTech and Pfizer whether there is a way to increase supply beyond the initially contracted 300 million doses, Stefan De Keersmaecker, a health-policy spokesman, said Monday. He declined to comment Tuesday about the details of the extra shots being sought.

Pfizer and BioNTech are pursuing all their options to boost production capacity for the vaccine beyond the 1.3 billion doses originally planned for this year, Sahin said in an interview last month. The CEO said he was confident that would be possible, saying the partners would probably know by January or February whether and how many additional doses they would be able to offer.

European leaders have also come under fire for how the existing doses have been distributed. In France, administrative red tape and a lack of nursing home staff hobbled the early days of the vaccine campaign. Meanwhile, German Chancellor Angela Merkel is being criticized for tasking the EU with centralized negotiations instead of striking out on her own sooner to get more of the vaccine for Germany itself.