The European Medicines Agency did not say what was targeted in the cyberattack or when it happened — although German firm BioNTech said the hackers "unlawfully accessed" vaccine approval documents.
"EMA has been the subject of a cyberattack. The agency has swiftly launched a full investigation, in close cooperation with law enforcement and other relevant entities," the agency said.
The EMA added that it "cannot provide additional details whilst the investigation is ongoing," but said further information would be released "in due course."
The agency, which is the EU's regulator of medications, did not provide details about what was targeted or when the attack took place.
Just after the announcement, however, German pharmaceutical firm BioNTech and US pharma giant Pfizer said some documents on their jointly-developed vaccine were accessed during the cyberattack.
In the joint statement, the companies said the EMA told them that "some documents relating to the regulatory submission for Pfizer and BioNTech’s COVID-19 vaccine candidate [...] had been unlawfully accessed."
The companies added that the hackers did not breach BioNTech or Pfizer systems, and that there was no evidence at this time to indicate that the personal data of study participants had been accessed.
The cyberattack comes amid concerns about hackers targeting coronavirus research and other cybercrimes related to the pandemic.
The United Kingdom accused Russia-based hackers of targeting laboratories carrying out vaccine research in July. Other cybercriminals have attempted attacks on companies working to develop vaccines including AstraZeneca, Johnson & Johnson, Novavax and others.
Currently, the Amsterdam-based regulator is rushing to analyze several coronavirus vaccine candidates.
A decision on the BioNTech-Pfizer vaccine is set to be announced by December 29 at the latest. A ruling on Moderna's vaccine is due to follow by January 12.
The EMA is also reviewing the AstraZeneca-Oxford University vaccine, although it's not yet known when that one could be approved.
The UK already issued emergency approval for the BioNTech-Pfizer vaccine on December 2 and has started its vaccination program. Regulators in the European Union and the United States have not yet approved a vaccine.
On Wednesday, EMA director Emer Cooke voiced optimism about the bloc approving the BioNTech-Pfizer vaccine soon.
"We are more and more convinced by the available test results," Cooke told Dutch news program "Nieuwsuur."
She added that experts were working around the clock to check the tests, but that "no concessions" would be made in terms of security.
rs/msh (AFP, Reuters, dpa)