The Sanofi effort is particularly promising, given the company’s previous experience combating Severe Acute Respiratory Syndrome, a virus that resembles the one causing COVID-19. If clinical trials go well, Sanofi expects to make 600 million doses annually of a COVID-19 vaccine.

However, even if that target were reached in 2021, it would cover less than 10% of the world’s population. And even if a manufacturer such as Sanofi could meet U.S. demand in 2021, it is not obvious that it would or should devote most of its supply to the United States.

Finally, a previous collaboration between Sanofi and the U.S. government offers a cautionary note. Sanofi began working with federal partners on a Zika vaccine in 2016. The partnership collapsed in 2017, though, due to declining disease prevalence and haggling over price.