French drugmaker Sanofi and Britain's GlaxoSmithKline said they had started a clinical trial of their protein-based Covid-19 vaccine candidate, and aimed to reach the final testing stage by December.
If the results are conclusive, Sanofi and GSK hope to get the vaccine approved in the first half of next year.
The trial is currently in a "Phase 1/2 study" aimed at evaluating the safety, tolerability and immune response of the vaccine in 440 healthy adults across 11 investigational sites in the United States.
The vaccine candidate uses the same recombinant protein-based technology as one of Sanofi's seasonal influenza vaccines. It will be coupled with an adjuvant, a substance that acts as a booster to the vaccine, made by GSK.
The two companies are scaling up manufacturing in order to be ready to produce up to one billion doses in 2021.
Drugmakers and government agencies worldwide are racing to develop vaccines and treatments for Covid-19, the illness caused by the new coronavirus, which has claimed more than 861,000 lives and crippled economic activity around the globe.
Sanofi and GSK are not the first in the race - several vaccine candidates have already reached the final, wider testing stage known as "Phase 3" - but they believe their respective experience in the fields of vaccines is an advantage.
The French group is also working on another vaccine candidate to prevent Covid-19 with US company Translate Bio which will rely on a different technology called mRNA.
In an interview with Reuters last week, Sanofi's CEO Paul Hudson said readings of preclinical data had increased the group's confidence in its two coronavirus vaccine candidates.
Sanofi and GSK have secured deals for the vaccine-plus-adjuvant with the United States and Britain, and are in advanced talks with the European Union to supply it with up to 300 million doses.
They also plan to supply COVAX, a Covid-19 vaccine and treatment allocation plan co-led by the World Health Organization (WHO) that aims to help buy and fairly distribute shots across the globe.
Earlier this month, Sanofi said a rheumatoid arthritis drug, Kevzara, had failed as a Covid-19 treatment.