A German company working with US pharmaceutical giant Pfizer has begun human trials of a potential <a href=”https://www.cnn.com/2020/03/31/health/what-is-coronavirus-covid-19-wellness/index.html” target=”_blank”>Covid-19</a> 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