Which vaccine is most important for preventing pneumonic plague outbreaks?

Historically, plague vaccines were developed, but there is no widely used modern plague vaccine for the general population. Pneumonic plague is a rare but very severe form caused by Yersinia pestis and can spread person to person through respiratory droplets. Current control depends on rapid diagnosis, antibiotics, contact management, and public-health response rather than routine vaccination. That makes plague a striking example of a serious disease without a standard mass vaccine today.