what is the context of that question?

The Google News webpage (https://news.google.com/) doesn't let one filter by date.

However, if one goes to Google's regular homepage (https://www.google.com/), one can do a search, then under "Tools" set a date filter on results, then click on "News", then under "Tools" choose "Sorted by Date".

When I search for "russia plague" there and keep cranking the date back, when I get back to "Before Oct 1, 2026", the first hit I get there is from The National News Desk:

https://thenationaldesk.com/news/americas-news-now/us-monitoring-suspected-pneumonic-plague-case-in-russia-one-reported-death-united-states-public-health

It's reporting that the Russian governor of the region in question made an announcement.

So assuming that the times are accurate, I'd guess that this is probably the first English-language source (or at least the first one that Google News indexed), that the initial source in any language was in Russian-language media, and possibly the Russian government, if the information didn't get out from Russian-language media prior to the governor's announcement:

WASHINGTON (TNND) — The death of a worker at an anti-plague laboratory in Russia has prompted officials to quarantine at least one hospital facility and place nearly 200 people under medical observation, according to reports.

The female staffer died last week from “pneumonia of undetermined” origin, according to the regional governor Igor Kobsev. Dozens of people were reportedly in isolation after the laboratory worker, who was dedicated to studying the plague and other infectious diseases, died of an undisclosed illness. Local media identified the researcher as Darya Shipilova, a 28-year-old lab technician at the Irkutsk Research Anti-Plague Institute in Siberia.

If you want to look in Russian-language media, you're probably going to either need to play around with Russian-language translated terms or find a Russian speaker to help, and I'm not sure whether Google News indexes it.

You might also have luck with Twitter (or, if that's blocked in Russia, whatever analog Russians use). I don't know if that can do date-filtered searches, but I'd imagine that it'd be a useful tool for seeing chatter about something.

How do you mean? There was an outbreak of some version of "the plague" in Siberia

I guess its sort of 2 questions:

1. What was the first public report of the Siberian plague outbreak
2. What/who was the source?

Outbreak?