French pharma giant Sanofi said Tuesday that international Phase 3 clinical tests of its Kevzara drug for serious Covid-19 cases had proved inconclusive and it was halting the trial.

The Phase 3 test -- normally the last before official approval for use -- "did not meet the primary or secondary evaluation criteria compared with a placebo, and in both cases, compared with established hospital care," it said in a statement.

Sanofi said neither it nor its American partner in developing the drug, Regeneron, "envisage further clinical tests of Kevzara for the treatment of Covid-19."

Although Kevzara "did not give us the results we were hoping for, we are proud of the work done by our team," Sanofi global research head Dr. John Reed said in the statement.

Since the outbreak of the coronavirus pandemic late last year in China, it has claimed more than 800,000 lives and caused huge economic damage, sparking a global race to find a vaccine and effective treatments. 

Sanofi is one of many companies developing a vaccine but scientists are cautious in saying that at best, one may only be available by the end of this year for initial use.