Novavax, Moderna stocks fall after WHO calls plague risk 'low'

Novavax stock ( NVAX ) fell on Tuesday after a World Health Organization (WHO) spokesperson told reporters that there was a "low" risk of a plague epidemic, after a 28-year-old woman who worked in a Russian anti-plague laboratory died last week .

Shares of Novavax fell nearly 10%, pulling back from a 20% gain the day before that was fueled by concerns about a potential outbreak. Moderna ( MRNA ) stock fell 7%, giving back all its gains from Monday. BioNTech ( BNTX ) fell 2%, while Pfizer ( PFE ) was little changed.

A worker at the Irkutsk Anti-Plague Institute of Siberia and the Far East died of "pneumonia of undetermined" origin last week, raising concerns about a potential global health scare.

The WHO is investigating whether the death was due to pneumonic plague, a highly contagious disease caused by the bacterium Yersinia pestis. Pneumonic plague is curable with antibiotics if caught early, but it can be fatal within 24 hours of onset if left untreated, WHO spokesperson Christian Lindmeier said.

Lindmeier noted that Shipilova's workplace was "an institute that studies dangerous pathogens, including plague, in a part of Siberia where plague occurs naturally in wild animals."

Lindemeier said WHO had identified and tested the worker's contacts and did not detect plague or pathogens of dangerous infectious diseases.

"None to date have shown symptoms of illness," he said of the contacts.

WHO "estimates the risk to be moderate to low for Irkutsk, a low risk for the Russian Federation as a whole and very low for the WHO European region," Lindmeier added.

US officials have called on Russia to be more transparent about the incident. Russian authorities reportedly put one hospital facility and dozens ‌of people under quarantine.

"I think it's incumbent upon Russia to obviously share more ‌information with the ⁠world," Secretary of State Marco Rubio said on Tuesday. "We're watching it very closely, hour by ⁠hour."