Anime fans dressed up in robes, armor and colorful wigs pushed their way through throngs of people to reach the entrance of New York City’s three-day confab of Japanese pop-culture enthusiasts.

While the event required vaccinations and indoor masking, attendees said people pushed past checkpoints and pressed together in large crowds unmasked. Now, the city is faced with warning 53,000 people who came to the November convention to ask them to immediately get tested for COVID-19 after an attendee contracted one of the first confirmed infections of the omicron variant in the U.S.

There’s no indication yet that there was indeed a superspreader event at Manhattan’s Javits Center, but the massive gathering underscores how even the best-laid plans for strict health protocols can wobble when tens of thousands of people amass and pent-up demand for normalcy and excitement overtake health precautions.