Ubisoft has officially revealed Rainbow Six Quarantine, a co-op PvE spin-off to Rainbow Six Siege. Unfortunately, that's almost all that we know—despite making the announcement on its E3 stage today, Ubi didn't have much else to say beyond the brief teaser above.
It's likely that Quarantine is based on popular Outbreak mode from Siege's Year 3, a temporary mode that seemed like a weird thematic departure at the time, but with hindsight was clearly a proof-of-concept.
Ubisoft has big ambitions for Quarantine. "What Siege is to the PvP shooter genre, we will be to PvE co-op," Ubisoft said. Quarantine is being developed by a new team inside Ubisoft Montreal, the developers of Rainbow Six Siege. The teaser video doesn't show any gameplay, but we can assume a certain amount of similarity to Siege's Outbreak mode.
The infection seen in the teaser looks similar to the black, messy texture of Outbreak's alien zombies. You can also see Siege operators Ela and Vigil, confirming that Quarantine takes place in the same world. Rainbow Six Quarantine is coming in early 2020, but you can already sign up to receive updates and get a chance to play an early beta.