(CNN) A German company working with US pharmaceutical giant Pfizer has begun human trials of a potential Covid-19 vaccine that could supply millions by the end of the year, according to the two firms.

Pfizer says it will begin testing the experimental vaccine in the United States as early as next week, and says a vaccine could be ready for emergency use in the fall, the Wall Street Journal reported on Tuesday.

Mainz-based BioNTech reported that the first cohort of participants had been given doses of the potential vaccine, BNT162, in a Phase 1/2 clinical study in Germany.

"Twelve study participants have been vaccinated with the vaccine candidate BNT162 in Germany since the start of the study on April 23, 2020," the company said in a statement.

No information on the results is currently available. BioNTech said around 200 healthy volunteers aged 18 to 55 years old would be given doses ranging from 1µg (microgram) to 100µg to find the optimal dose for further studies.

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