Two big unknowns stand in the way of determining how serious the plague threat in Russia is and whether travel advisories, restrictions at U.S. ports of entry or other precautions are warranted.

• We still don't know which pathogen killed a Russian researcher, or how well contained it is. Why it matters:

Though public health experts say there's no cause for Americans to panic, the episode serves as a wake-up call emphasizing the nature of global biological threats and the need for pandemic preparedness. State of play:

A worker at the Anti-Plague Research Institute of Siberia and the Far East recently died after contracting pneumonia. There are conflicting accounts of how she got sick and whether she was infected with pneumonic plague, which is almost always deadly without prompt treatment with antibiotics.

• Secretary of State Marco Rubio said Monday that the administration is closely monitoring the situation, adding, "I don't think it's cause for alarm, but it is cause for focus and a cause to just keep an eye on.

And we're doing that." • If a response is required, "the playbook for these instances is very well defined," David Mansdoerfer, a former health official in the first Trump administration, told Axios.

• "Traditionally, the precautionary measures the government would take would be via a travel advisory from [the State Department]," he said, adding the U.S. already has its most serious travel warning in place for Russia due to the war with Ukraine.

• It would also contact U.S. citizens in the affected area with guidance, and the Centers for Disease Control and Prevention would follow up with a travel health notice, Mansdoerfer said.

• "The government would then focus on [Customs and Border Protection] ill traveler rules" that can include stopping high-risk individuals from boarding flights or flagging health officials if they land at a port of entry. At that point, "it becomes a CDC protocol-driven process," he added. The intrigue:

If the Russian worker did die from pneumonic plague, experts say there's a possibility that it was a genetically altered version that behaves differently than the treatable strain.

• That's just speculation at this point. But the prevalence of "gain-of-function" research that enhances pathogens to study them and Russia's known development of biological weapons make it impossible to rule out.

U.S. preparedness efforts will focus first on getting as much detailed information as possible because officials first need to understand what is going on to prepare for it, said Tom Inglesby, director of the Johns Hopkins Center for Health Security.

• "It's really critical to get the diagnosis right. There are conflicting stories around it," Inglesby said, noting that while there are substantial supplies of antibiotics in government stockpiles and pharmacies, there's still the possibility the strain is resistant to them.

Another key unknown is if pneumonia believed to be linked to plague has spread in the community. So far, reports suggest it's limited to the lab scientist who died while others in the community are under close monitoring.

• "Pneumonic plague does not normally cause large outbreaks in modern times, it happens rarely but it's very uncommon," Inglesby said. "If many people in that city do get sick, that would call into question the diagnosis, or raise concerns about something else going on."

• "Getting the real story, the true facts of the situation out in the open is critical to everything else that follows in the response," he added.

Asked whether he's concerned, President Trump on Monday said: "Somehow those microbes have gotten stronger and smarter. They're like an army ... even with great advances, the germs have really become relatively stronger than they were, and things that used to work on pneumonia don't work as well anymore."

Friction point: Determining whether the incident resulted from legitimate plague research as opposed to a weapons program is important, considering the still-heated debate over COVID's origins and the Russian institute's connection with the nation's biowarfare apparatus.

• There's no credible evidence that the deceased worker at the Russian institute was involved with research on a weaponized or engineered strain. In fact, some reports state she had recently traveled to regions along the Mongolia-Russia border, where plague naturally occurs in animals.

• The institute where she worked was established as part of an anti-plague network and was mainly responsible for surveillance of dangerous pathogens. But it developed vaccines and diagnostics for pathogens that were modified by the military, according to the James Martin Center for Nonproliferation Studies.

A 2024 State

Department assessment concluded Russia maintains an offensive bioweapons program and absorbed the old Soviet program and evolved it.

• The CDC says the Soviet Union in the 1970s and 1980s manufactured large quantities of antibiotic-resistant [the bacteria that causes plague] to be dispersed in the air as a bioweapon and that, in light of these and recent events involving terrorist organizations, the United States and other countries must be prepared for a bioterrorism attack involving .

Zoom out: Pneumonic plague cases are rare but not unheard of, including in the U.S.

• Last year, the CDC launched a pneumonic plague investigation in Arizona after a young adult male died after exposure to two ill cats. Officials identified 46 potentially exposed persons, who were given antibiotics.

The bottom line: In the most optimistic scenario, Russia has responded with an abundance of caution to a one-off deadly infection that hasn't spread.

• But there's too much that still needs to be verified to draw any conclusions.