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After the first person known to have become infected with the Omicron variant in the United States was revealed to have attended a 53,000-person anime convention in Manhattan, concerns quickly mounted that the event had sown the seeds of a major coronavirus outbreak.
But a new study released on Thursday by the Centers for Disease Control and Prevention suggested that a combination of good air filtration, widespread vaccination and indoor masking had in fact helped prevent the anime convention in November from becoming a superspreader event.
The share of attendee tests that came back positive was similar to the share of coronavirus tests that were positive across New York City around the same time, the C.D.C. said. What’s more, the few positive samples that were genetically sequenced were largely of the Delta variant, not Omicron.
And conventiongoers who became infected were more likely than those who tested negative to have gone to bars, nightclubs or karaoke clubs.
Still, the C.D.C. said that the virus’s spread at the convention could have been much worse had it been held after Omicron became dominant in the city, given that the variant is so contagious and capable of spreading among the vaccinated. At the anime convention, the C.D.C. said in a separate report on Thursday, the only documented Omicron infections were in a single cluster of at least 16 positive cases.
The first study relied largely on people who came forward for testing after the event, which introduced potential biases: Those people could have been more cautious than the average convention attendee, or more inclined to report cautious behaviors. Health officials had urged attendees to get tested. The C.D.C. could only look for cases among people on a registration list of ticket buyers, which did not account for the full number of attendees.
The agency’s findings matched those of New York City contact tracing officials, who said in early December that they had not found signs of widespread transmission at the anime convention.
In the aftermath of the event, held at the sprawling Javits Center, the convention organizers came under scrutiny as people reported seeing attendees flouting masking rules and pushing past checkpoints.
But among attendees who were tested, the C.D.C. said, “evidence of widespread transmission during the event was not identified.”
The study drew on test results identified through health department surveillance systems for 4,560 attendees. Of those, 119 people — 2.6 percent — tested positive. Researchers also sent online surveys to attendees asking about their test results, symptoms and activities during the convention.
The anime convention required attendees to have received at least one vaccine dose. The C.D.C. said that among attendees who could be matched with test and vaccination data in health department surveillance systems, 85 percent had completed their primary vaccination series, another 12 percent had received a booster dose and 3 percent were partly vaccinated.
The C.D.C. study also credited the convention hall for being outfitted with HEPA filters, which have been shown to efficiently remove coronavirus particles from the air.