With U.S. giant Johnson & Johnson, the European Union is negotiating a supply of 200 million doses of its potential vaccine, the sources said, adding that additional supplies may also be available.
The bloc is also planning to secure in the second half of next year 300 million doses of the potential vaccine developed by France's Sanofi in cooperation with British drugmaker GlaxoSmithKline Plc, the sources said.
Asked about the negotiations, Sanofi told Reuters it was in "advanced talks with the EU for the delivery of 300 million doses".
Negotiations were also ongoing, sources said, with U.S. firm Moderna, whose experimental Covid-19 vaccine showed this week it was safe and provoked immune responses in all 45 healthy volunteers in an ongoing early-stage study, according to U.S. researchers.