The WHO says the lack of a confirmed diagnosis remains a key uncertainty, with no sign of ongoing transmission.
Published On 10 Oct 2026
The World Health Organization (WHO) has said it still does not know what caused the pneumonia that killed a laboratory worker at a Russian plague research institute and that no case of plague has been registered.
Russia’s state health regulator told the WHO that tests on the worker and people who had been in contact with her were negative for the dangerous pathogens they tested for, the United Nations health agency said in a statement on Saturday.
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Her contacts still showed no symptoms, and no further linked cases of severe pneumonia had been found, the WHO added.
“Based on the information provided… WHO has not identified evidence of ongoing transmission associated with this event. A key uncertainty remains the absence of a confirmed diagnosis in the deceased laboratory worker,” it said.
What happened?
The worker fell ill and died in undisclosed circumstances on October 2, prompting authorities to quarantine about 200 people and stoking public health fears on social media.
Russian media named her as Darya Shipilova, a 28-year-old laboratory technician at the Irkutsk Antiplague Research Institute of Siberia and the Far East, in the Siberian region of Irkutsk.
Pneumonic plague, a lung infection caused by the bacterium Yersinia pestis, which is usually found in small mammals and their fleas, was suspected early on.
The governor of neighbouring Buryatia said the woman had “died, maybe of the plague”.
Russia’s health watchdog Rospotrebnadzor said she had been diagnosed with “pneumonia of unknown aetiology”.
Russian authorities said the worker was appropriately vaccinated and that no microorganisms linked to her work were found in her body. They say post-mortem tests did not detect plague.
On Thursday, Russia said it had completed health checks on all her contacts and had given the WHO all the information.
A local official said on October 6 that 60 percent of those placed in quarantine had already been released.
WHO chief Tedros Adhanom Ghebreyesus asked Russia on Wednesday to respond to media reports of a second employee with pneumonia of undetermined cause. Russia dismissed the reports as “false information”.
The United States has also called on Russia for transparency.
Global health officials have been extra alert to deadly pneumonia cases of unknown cause since the COVID-19 pandemic, which began with a cluster of fast-spreading, fatal respiratory illness in China.
The cause of individual pneumonia cases often cannot be determined.