One after another, desperate New Yorkers trekked to the back of a line that snaked around corners and down several blocks in Brooklyn’s Sunset Park neighborhood on Thursday evening. It was chilly and dark, but the wait was worth it for hundreds lured by a message promising a rare find: a leftover dose of coronavirus vaccine.

“We need to give out 410+ doses in the next 4 hours at Brooklyn Army Terminal (by 7 p.m.), taking anyone in community age 18+, walk ins, or earlier than scheduled,” read the WhatsApp message.

By early evening, the New York mayor’s office took to Twitter to warn that the memo was “misinformation” and that “there is NOT available vaccine for people without appointments.”

But that news didn’t make it in time for the crowd swarming the 24/7 site, where staff members quickly became overwhelmed dealing for hours with the confused masses.

The chaotic scene reflects the country’s disorganized and slow vaccine rollout. So far, roughly a third of the vaccines distributed throughout the country have been used, according to the Centers for Disease Control and Prevention. At least 11.1 million people have received one dose of the vaccine and 1.2 million people are fully vaccinated, according to The Washington Post’s tracker. At least 688,000 New Yorkers have received the first dose. The state received 1.6 million first doses.

It’s not surprising some New Yorkers would believe the message. Throughout the country, some pharmacies and hospitals have offered leftover doses with a dwindling shelf life to walk-ins. In D.C., people have camped outside of pharmacies, hoping to bag an inoculation. But other institutions have made detailed contingency plans, like the Nashville Metro Public Health Department, which has a standby list so that extra doses aren’t wasted.

It’s still not clear who started the rush on the Brooklyn Army Terminal on Thursday. The anonymous message, which is time-stamped at 3:40 p.m., quickly spread on Twitter, group chats and Slack channels.

It didn’t take long for city officials to debunk the rumor. At 5:29 p.m., Bill Neidhardt, press secretary for Mayor Bill de Blasio (D) tweeted out a warning and said authorities would tell the crowd to leave. “We are sending people to Brooklyn Army Terminal to ask people in line to return home if they don’t have appointments,” he wrote.

Neidhardt tweeted that the WhatsApp message “did all it could to look official,” and he acknowledged that many sites do have leftover doses — but certainly not 400, as the message said.

But despite those claims from the mayor’s office and other city and state officials who said the message was “bogus,” some people who queued said officials told them the site was taking walk-ins.

“I waited in line until a doctor came out and she confirmed that they had been taking walk-ins, but that it was a one-time event that they would not be repeating,” Cecilia Nowell, a freelance reporter, tweeted in response to Neidhardt.

In a video posted on Twitter, a man recorded a woman he said was a doctor at the site echoing Nowell’s comment. “Today was an exception,” the woman said in the video. “It was a single event. Unfortunately, we are not able to offer walk-ins anymore.”

Another video showed a health worker saying that the site had accepted walk-ins earlier, but that they were too understaffed to handle the crowd. “There were extra vaccine, but we don’t have the man power,” she said.

The endless line outside the Brooklyn Army Terminal alarmed people who showed up for their scheduled appointments. As of Monday, teachers, education workers, first responders, people over 65, public safety workers and public transit workers in New York are eligible for the vaccine.

Ashley Privett, a 29-year-old educator at a museum, said she drove to her 6:30 p.m. appointment but arrived late because of traffic outside the site.

“I was at a dead stop 8 or 10 blocks away,” she said in an interview with The Washington Post. “I couldn’t figure out what was going on — I thought there was an accident.”

As she walked to the gate, she saw 300 to 400 people lined up and police guarding the entrance. Panicked, Privett asked people in line if they had appointments, but they told her they were there for the extra doses.

“Even workers were confused,” Privett said. “I spoke to a staff person and she said, ‘We’re not honoring appointments.’ I freaked out.”

Soon afterward, a woman holding a bullhorn and flanked by two police officers went to the line and instructed people with appointments to line up separately and told the rest of the crowd that they were not accepting walk-ins.

“Once we got inside, everyone moved like clockwork,” Privett said. “It was just chaos outside the fence.”

Privett said the scene was a reminder of how badly people want to get inoculated.

“I think people are desperate to get a vaccine,” Privett said. “I think a lot of people just really want to get back to whatever their lives were pre-March of last year, which I totally understand. But this is not the method to do that.”