Sanofi and GSK said they had reached an agreement with Britain to supply it with up to 60 million doses of a potential COVID-19 vaccine, and that discussions with other governments were ongoing.

No vaccine has yet been approved to treat or prevent COVID-19, the respiratory disease caused by the new coronavirus which has killed more than 659,000 people and triggered economic havoc worldwide.

Financial terms of the agreement were not disclosed. Sanofi and GSK, which had first teamed up in April, confirmed in a statement that regulatory approval for their vaccine could be achieved by the first half of 2021 if clinical data was to be positive.

The first clinical trials are expected in September.

The vaccine will be developed by combining Sanofi’s S-protein COVID-19 antigen and GSK’s pandemic adjuvant technology.

Adjuvants are efficacy boosters that play a vital role in many vaccines. An adjuvant is added to some vaccines to enhance the immune response, and has been shown to create a stronger and longer lasting immunity against infections than a vaccine alone.

Sanofi and GSK said other discussions with the European Union, Italy and France to supply their vaccine were ongoing.

Sanofi and GSK are hoping to clinch a deal soon to provide 300 million doses to the European Union.

Two sources told Reuters that negotiations stalled because the company wanted to secure an upfront payment for the entire stock while the EU would rather delay payments until the vaccine has passed large clinical trials.