The USA is worried after a worker at a research laboratory in Siberia died. She died of severe pneumonia. Local reports say she may have broken a test tube of pneumonic plague bacteria. Officials are checking people who were in contact with her. Russia said the woman's death was from "pneumonia of an unknown origin" and not plague. The USA said there was no "cause for alarm". However, it said officials should "keep an eye on it".

Pneumonic plague can be deadly. It attacks the lungs. It can kill in 18 hours. It also spreads quickly. It moves through the air when someone coughs. The disease can be treated with medicine if drugs are given when symptoms appear. Pneumonic plague is different from COVID-19, which is caused by a virus. A microbiologist said: "Pneumonic plague can spread from person to person, and that is why there is the concern around this."