COVID-19 cases in South Dakota are spiking following the Sturgis Motorcycle Rally earlier this month.

The annual event took place in Meade County, where hundreds of thousands of motorcyclists gathered from Aug. 6-15, CBS News reports. On Aug. 4, there were 657 active cases in the state, with 3,655 active cases being reported on Aug. 25—a 456 percent surge.

The weekly positivity rate in the week leading up to the event was 10.38 percent, and the week before that was 6.10 percent. On Aug. 24, the weekly positivity rate shot up to 38.8 percent, which dropped slightly last week to 34.2 percent.

Vaccines weren’t required to attend the rally. “We’re not going to start checking papers. I mean, that’s not really an American way,” Daniel Ainslie, city manager of Sturgis, told CBS. Sturgis has a population of 7,000; only about 28 percent of the county is currently vaccinated.

Daniel Bucheli, spokesman for the South Dakota Department of Health, told the outlet, “COVID-19 case spikes are following a national trend being experienced in every state, not just South Dakota.”

“Regarding cases surrounding the Sturgis rally, our department has only been able to link 39 cases directly to this event,” Bucheli continued. “It is important to mention that Meade County currently has a lower vaccination rate than other counties in the state. Fully vaccinated residents in this county is 45.1%, versus 55.94% for the state as a whole.”

The rally took place last year and was dubbed a superspreader event, with over 100 cases later linked to the rally in at least eight states. Wearing masks was not enforced that year, either.