In principle, yes, that would have been a good example of government intervention to stabilize market expectations. However, in practice that isn't what happen

In principle, yes, that would have been a good example of government intervention to stabilize market expectations. However, in practice that isn't what happened. First, this is a line of research that began in January well before the pandemic actually got out of hand. Researchers started developing a vaccine as soon as there were indications that the transmission rate and fatality rate would be high. Second, Operation Warp Speed was announced in early April. This was already long after the pandemic had gotten out of hand.