The World Health Organization 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.

In a statement on October 10, the UN health agency said Russia’s state health regulator had told it that tests on the worker and people who had been in contact with her were negative for the dangerous pathogens they tested for. The WHO added that her contacts showed no symptoms and no further linked cases of severe pneumonia had been found.

What happened in Siberia

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 in Siberia.

Initial reports suggested her death was caused by pneumonic plague, a lung infection caused by the bacterium Yersinia pestis. Russia’s health watchdog Rospotrebnadzor said she had been diagnosed with pneumonia of unknown origin. Russian authorities said the worker was appropriately vaccinated, that post-mortem tests did not detect plague, and that no microorganisms linked to her work were found in her body. The Kremlin dismissed the early reports as largely false.

WHO seeks more answers

WHO chief Tedros Adhanom Ghebreyesus asked Russia on October 7 to respond to media reports of a second employee with pneumonia of undetermined cause. Russia dismissed those reports as false information. The WHO said that, based on the information provided, it had not identified evidence of ongoing transmission associated with the event, but noted that a key uncertainty remains the absence of a confirmed diagnosis in the deceased worker.

On October 8, Russia said it had completed health checks on all her contacts and 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. The United States has also called on Russia for transparency, and the WHO continues to monitor the situation.