There is diversification across a number of fronts, and I would say that number one is the various platforms. Pfizer and Moderna have a similar platform. Then there's Johnson & Johnson and AstraZeneca, with the viral vector, and for the more traditional protein subunit, there are the Novavax, Medicago and Sanofi candidates. There's diversification there, which is important, because it wasn't clear which vaccines would be successful early on, and indeed some are still going through the hurdles.
There were also questions about the ability of industry to scale up: Even if you have a successful vaccine, how quickly can you manufacture at scale? Again, diversification is important. The location of manufacturing and getting some spread there is important as well.