Developing a Covid-19 vaccine in record time will be tough. Producing enough to end the pandemic will be the biggest medical manufacturing feat in history.

That work is underway.

From deploying experts amid global travel restrictions to managing extreme storage conditions, and even inventing new kinds of vials and syringes for billions of doses, the path is strewn with formidable hurdles, according to Reuters interviews with more than a dozen vaccine developers and their backers.