Universal coronavirus vaccines: the time to start is now.

The continued explosive spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) despite aggressive public health measures has triggered an unprecedented international vaccine effort. However, correlates of protection, which can help guide intelligent vaccine design, are not known for SARS-CoV-2. Research on influenza immunity and vaccine development may provide valuable lessons for coronavirus efforts, especially considering similarities in rapid evolutionary potential. The apparent inevitability of future novel coronavirus outbreaks must prompt work on a universal coronavirus vaccine.