The European Union will keep the details of its contracts with Covid-19 vaccine makers secret while negotiating with them, the bloc's commissioner for health said Thursday.

"We are bound by the confidentiality clauses of the contract, and disclosure of any confidential information at this moment in time undermines the ongoing negotiations that we have with companies," Stella Kyriakides told the European Parliament.

The European Commission has negotiated or is in the process of negotiating pre-purchase agreements with seven manufacturers of proven or potential Covid-19 vaccines.

Two of the vaccines, ones made by BioNTech/Pfizer and by Moderna, have been authorised for use in the EU, and the Commission hopes others will follow.

The bloc has already secured advance order contracts for two billion doses of those vaccines, enough for twice the EU's population of 450 million given that most of the vaccines require two doses, to be administered weeks apart.

But a slow rollout in member countries, coupled with the secrecy obscuring the terms of the contracts, have contributed to the political pressure building against EU governments and the Commission.

Kyriakides said, however, that the confidentiality clauses would be respected for the time being.

"When the time's ready within the contractual constraints (we'll) explore making information of these contracts available to nominated members of the Parliament with specific arrangements... once the sensitive ongoing negotiations are concluded," she said.

Kyriakides added that the confidentiality was part of an EU strategy to get the most cost-effective result.

By negotiating on behalf of -- and in coordination with -- the EU's 27 member countries, "it reduces cost and it gives us a stronger negotiating position," she argued.

The EU has sealed deals with BioNTech/Pfizer, Moderna, AstraZeneca, Johnson & Johnson, Sanofi-GSk and Curevac, and it is in talks with Novavax.

The Commission has been criticised in the German media, accused of under-buying vaccines developed by German outfits BioNTech and Curevac to proportionally boost those made by French group Sanofi.

But Kyriakides strongly denied that, noting that the negotiations started early last year when no data was available as to which of the potential vaccines might turn out to be effective.

Europe, she said, "did not put all its eggs in one basket," and the advance-order contracts were struck in agreement with member states.

The Sanofi contract was based on "the type of vaccine, the time factor, the price, the proven capacity for safe mass production and distribution, and the issue of liability," she said.

"The way the member states moved with this vaccine has nothing to do with this being produced in France."

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ASTRAZENECA

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BioNTech

JOHNSON & JOHNSON