The chief executive of Germany's BioNTech, Ugur Sahin, said the biggest challenge facing it and partner Pfizer now that their COVID-19 vaccine is authorized for use in the United States will be to scale up manufacturing to meet the huge demand. Subscribe: http://smarturl.it/reuterssubscribe Reuters brings you the latest business, finance and breaking news video from around the globe. Our reputation for accuracy and impartiality is unparalleled. Get the latest news on: http://reuters.com/ Follow Reuters on Facebook: https://www.facebook.com/Reuters Follow Reuters on Twitter: https://twitter.com/Reuters Follow Reuters on Instagram: https://www.instagram.com/reuters/?hl=en