It should go without saying, but if you are unvaccinated and have symptoms of COVID-19, or have no symptoms but test positive, then you should not go into a small, crowded bar without a mask to celebrate its reopening.

Seriously.

Four infected young adults — three who felt sick and one who had tested positive the day before — threw caution into beer cups in rural Illinois in early February. That set off the kind of super-spreader event that public health officials are worried about, as they brace for the fallout of college spring breaks, Easter and Passover gatherings, and the reopening of indoor establishments.

The Illinois event, detailed in the U.S. Centers for Disease Control and Prevention’s latest weekly report, had all the now-familiar ingredients for far-flung transmission: about 100 unvaccinated people — predominantly young men — gathered in a poorly-ventilated, 2,800-square-foot bar. They later admitted in interviews with local health department contact tracers that their mask use was “inconsistent.”

The result was 46 cases of COVID-19 — enough to make the county’s seven-day average of cases per 100,000 residents jump from 42 to 87.

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Of those 46 cases, 26 were bar patrons, three were bar staff, and 17 were their “secondary” contacts, meaning people in homes, a nursing home, and a school. Although only one individual, a nursing home resident, was hospitalized, an elementary school with 650 children shut down for more than a week.

The CDC has described (and the media has reported) similar super-spreader events linked to restaurants, weddings, and night clubs, so by now, the public can’t really plead ignorance. But as vaccination expands, pandemic fatigue deepens, and indoor venues reopen, a false sense of security may be setting in.

“The epidemic is still here, and it’s still deadly, so I want to remind people: Don’t let your guard down too early,” Philadelphia’s Health Commissioner Thomas Farley said at a virtual news conference on March 16, the one-year anniversary of the city’s decision to shut down nonessential businesses and government agencies.

The CDC report noted that risk-taking in a bar can affect not just the patrons and employees, “but can also affect an entire community.”