WHO says the cause of a Siberian lab worker’s fatal pneumonia remains unknown, but reports no evidence of ongoing transmission after thousands of tests

The World Health Organization says it has found no evidence of ongoing transmission after a 28-year-old researcher at Russia’s Irkutsk Anti-Plague Research Institute died of severe pneumonia on October 2. The cause of Darya Shipilova’s illness remains undetermined, and WHO says the lack of a confirmed diagnosis limits its assessment.

Russian authorities told WHO that Shipilova and her contacts tested negative for the high-threat pathogens examined, including plague. They said she had been vaccinated against pathogens handled in her work and that no microorganisms associated with her research were found in her body. All identified contacts remained symptom-free; their medical monitoring was completed, and no additional linked cases of severe pneumonia were reported. Russia said it had completed examinations of contacts and shared information with WHO. More than 5,500 laboratory tests found no high-consequence or dangerous pathogens, according to the agency. About 200 people were initially reported to have been placed under precautionary measures. WHO said a laboratory-associated exposure could not be fully ruled out and called for further investigation; it does not advise travel or trade restrictions related to the event. Plague, caused by Yersinia pestis, occurs in wildlife in parts of Siberia, while human cases there are rare.