The World Health Organization (WHO) logo is displayed on a computer screen photographed using a kaleidoscopic filter, in Creteil, France, on May 11, 2026. Photo:: Getty Images

Reuters reported on the same day that WHO Director-General Tedros Adhanom Ghebreyesus made the request after Russian authorities attributed the first worker’s death to pneumonia of an undetermined origin. Around 200 people were initially placed in quarantine following the case.

"WHO has requested further information to clarify the cause of the severe pneumonia, the pathogen that prompted the public health measures," Tedros wrote on X. He added that the organization was also seeking clarification about media reports of a second employee with pneumonia of undetermined cause.

The first worker, identified as 28-year-old Darya Shipilova, died on October 2. Russia’s health watchdog reported that no plague cases had been detected among people who had contact with her, while a local official reported that 60% of those quarantined had been released.

Meanwhile, Western media outlets have reported that a second person in Siberia had died of plague, citing Russian media reports.

Russian authorities have not publicly identified the pathogen that caused Shipilova’s pneumonia or explained how she became infected. Pneumonia can result from multiple causes, including plague.

The WHO intervention follows growing international calls for Moscow to disclose more information about the case. Earlier, US Secretary of State Marco Rubio urged Russia to provide further details, while the incident also drew concern from US President Donald Trump.