Berlin (dpa) - US pharmaceuticals giant Pfizer and its German partner BioNTech have made further gains with their promising Covid-19 vaccine, announcing on Wednesday that the drug is 95-per-cent effective and passed a key safety milestone.

In a joint statement, the companies said that the experimental vaccine worked almost equally well among the crucial demographic group of people aged over 65, with an efficacy rate of over 94 per cent.

The results come at the conclusion of phase-3 testing, during which the developers also achieved a safety data milestone required for emergency authorization by the US Food and Drug Administration (FDA), the statement said.

No serious safety concerns were observed during the clinical trials, it added.

The companies plan to submit the drug to the FDA for approval "within days."

They expect to supply up to 50 million vaccine doses globally in 2020, increasing to up to 1.3 billion doses in 2021.

The mRNA vaccine, which uses a new form of medical technology drawing on the coronavirus' genetic code, must be kept at temperatures of minus 70 degrees Celsius, leading to doubts over its logistical practicality.

"Pfizer is confident in its vast experience, expertise and existing cold-chain infrastructure to distribute the vaccine around the world," the statement said.