Amsterdam (dpa) - Data from pharmaceutical companies Pfizer and BioNTech was targeted as part of a cyber attack on the European Medical Agency (EMA) in Amsterdam, the two companies announced in a joint statement early Thursday, after they were informed by the EMA.

According to the statement, "some documents relating to the regulatory submission for Pfizer and BioNTech's COVID-19 vaccine candidate, BNT162b2, which has been stored on an EMA server, had been unlawfully accessed."

It was unclear who was behind the attack.

An EMA spokesman said the organization was in contact with judicial authorities.

Pfizer and BioNTech emphasized that their respective systems had not been attacked. They also stated that, to their knowledge, no data on the test subjects had become accessible.

The pharmaceutical companies had been informed by EMA that the attack will have "no impact" on the approval procedure for the vaccine.

EMA Director Emer Cooke on Wednesday spoke encouragingly about the Covid-19 vaccine candidate. "We are convinced by the test results," she told Dutch broadcaster NOS.

The vaccine showed an effectiveness of 95 per cent among 30,000 people tested in the clinical trials.

A functioning coronavirus vaccine would be highly valuable in economic terms, as it permits countries to reopen their economies - which is why many states are participating in the race to find one.

Mikko Hyppoenen, security expert at the IT firm F-Secure, believes that ordinary criminals were not behind the hack, but that is come from a state intelligence service.

"Intelligence agencies have a job of defending their nations from outside threats," Hyppoenen said. "In that sense it's not surprising to see intelligence agencies try to steal vaccine research data, if they see Covid-19 as one of those outside threats, and if they believe that stealing research data makes it easier to defend their nations."