Pneumonic plague: the deadliest form of plague and why it spreads

A 28-year-old researcher died from an unidentified pneumonia at a Russian plague institute in Siberia, prompting quarantine of contacts and international monitoring by the WHO, US State Department, and CDC. The WHO says public health risk appears low. Pneumonic plague is a rare, fatal lung infection caused by Yersinia pestis bacteria and is considered the most dangerous plague form. It is the only type that spreads directly between people through respiratory droplets from coughing or sneezing, with symptoms appearing within 24 hours. Untreated, the disease is mostly fatal, but antibiotics given within 24 hours greatly improve survival chances. The last documented person-to-person transmission in the US was in 1924, and the most recent US death was in Arizona in July 2025.