A substantial Covid-19 outbreak that this week has sidelined the National Hockey League’s Ottawa Senators—despite the entire team being vaccinated—carries a warning for the coming months of professional sports: even with blanket immunization, pandemic disruptions are far from over.

The NHL announced the suspension of the Senators’ season through at least Nov. 20 after 10 players and one coach tested positive in recent days. The team says it is fully vaccinated, but hasn’t specified which shots players have received.

After nearly two years in which sports have delivered some of the most vivid case studies in public health, the Senators are presenting yet another: just how much Covid can still spread when a vaccinated group of people gather in poorly ventilated places and get up in each other’s bare faces. That’s a problem for every sport that plays indoors—and a warning for every coming holiday party.