France's Pasteur Institute is ending development of a COVID-19 vaccine with U.S. pharmaceutical company Merck after clinical trial results proved disappointing, it said on Monday.

The partners announced a tie-up last May and had been developing a jab based on an existing measles vaccine but it failed to prove its efficacy in phase one of clinical trials, the Paris-based institute said in a statement. 

The European Union had not yet concluded a deal with the Pasteur Institute for the delivery of vaccines. 

Sanofi, one of France's major pharmaceutical companies, has agreed a contract with the EU for delivery of 300 million doses of the vaccine it is developing with UK firm GlaxoSmithKline. 

That vaccine is not expected to be ready until much later in the year. 

More than a million people have now been vaccinated in France, but the number of people in hospital being treated for COVID-19 and those being admitted to intensive care remains high. 

Faced with new daily infections regularly above 20,000 and the threat of the spread of the more-contagious coronavirus variant first identified in the UK, the French government is considering adopting new restrictions. 

Prime Minister Jean Castex said on Monday "decisions will be taken this week" and that "all the health indicators are worrying."

There are meetings between the president and senior ministers scheduled for January 27, with one possible outcome being the reimposition of a national lockdown. 

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France came out of its second nationwide confinement on December 15 but immediately put in place a nightly curfew, which is still in operation. 

France's President Emmanuel Macron has suggested new measures are on the horizon in many EU states. 

"Today in France, we decided on a curfew at 6 p.m. every day and we restricted inbound travel from non-EU countries in order to stop the spreading of new variants," he said.

"And probably everywhere in Europe, we are moving in the coming weeks in order to adapt ourselves to better control the pandemic."