Transforming the site of what once was a Soviet-era car factory into a state-of-the-art facility churning out Russia's COVID-19 vaccine Sputnik V was the easy bit.

Making doses in bulk, finding qualified staff and getting equipment have been much bigger headaches for Moscow-based biotech firm R-Pharm and other private Russian companies picked to make the country's flagship shot to fight the pandemic.

President Vladimir Putin has trumpeted the vaccine around the world, and said in March that Russia had signed agreements for the production of 700 million doses abroad.