The British government has exercised an option to buy 40 million more doses of a Covid-19 vaccine being developed by the French-Austrian group Valneva for delivery next year, the company said Monday.

London announced in September it had agreed to buy as many as 190 million doses from Valneva in a deal worth up to 1.4 billion euros ($1.7 billion) as part of its innoculation drive against the virus.

Valneva said clinical tests of its vaccine, based on inactivated viruses, are expected to be completed within three months.

The doses would require standard refrigeration at two to eight degrees Celsius (36-46 Fahrenheit), meaning they would be easier to ship and store than vaccines from Pfizer and Moderna that have already been approved.

In a separate statement, the British government said the additional Valneva doses bring its potential total to 407 million doses over the next two years.

Clive Dix, head of the UK's vaccines taskforce, said the government wanted sufficient doses for "future flexibility should we need to revaccinate any of the UK population."

Britain has invested in the development of seven Covid-19 vaccines, Dix said.

Valneva is also in talks with the European Union to supply up to 60 million doses.