The US sent a formal diplomatic request to Russia for information regarding the pneumonic plague deaths, according to WaPo

Formal diplomatic requests for information are a routine but meaningful escalation step: they move a matter from press reporting into official channels and create a paper trail that obliges a response, however uncooperative. In past episodes involving public health incidents on adversarial territory, the sequence has tended to run from media disclosure, to a formal inquiry of exactly this kind, to either quiet bilateral handling or, if the matter touches treaty obligations on biological threats, referral to multilateral verification frameworks. Plague specifically sits in an awkward category: it is a naturally occurring endemic disease in parts of the region, but its capacity for person-to-person transmission means any unexplained cluster draws attention to biosafety and laboratory oversight questions, and states handling such inquiries have historically been guarded. The tell is the character of the response: a substantive, timely reply points toward containment of a natural outbreak, while stonewalling or a counter-narrative tends to extend the story and invite further scrutiny. For markets, episodes of this kind have generally been sentiment-level events rather than tradeable shocks unless they produce sanctions, treaty disputes, or evidence of a wider incident. Watch follow-on reporting from the same outlet and any confirmation from official US or Russian channels.