“It’s great to see a party of hundreds of thousands of people,” said Zoltan Vari, a rallygoer who was settling into his campsite on Tuesday after making the trek from Hungary.

He was eager to return to riding a Harley-Davidson through the Black Hills after missing last year. Vári evaded US tourism travel restrictions on Europe by spending two weeks in Costa Rica before making his way to South Dakota. He hopes one million people will show up. Typical attendance is around a half a million.

The city of Sturgis, usually a sleepy community of under 7,000, tried to calm things down last year, cancelling most city-sponsored events and promotion, but hordes of bikers showed up anyway.

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“The rally is a behemoth, and you cannot stop it,” said Carol Fellner, a local who worried that this year’s event would cause a fresh outbreak of cases. “I feel absolutely powerless.”

This year, the city is embracing the crowds. The state’s Republican governor, Kristi Noem, has given the rally her blessing and will appear in a charity ride. The event is a boon for tourism, powering over US$800 million in sales, according to the state Department of Tourism.

The rally is happening as other giant summer events – from state fairs to music festivals like Lollapalooza, which took place in Grant Park, Chicago, between July 29 and August 1 – are returning around the US.

In Wisconsin, health officials say nearly 500 coronavirus cases may be linked to the crowds that attended Milwaukee Bucks games or gathered outside the team’s arena – estimated as high as 100,000 one night – during their push to the National Basketball Association championship.

The Sturgis Motorcycle Rally’s defenders argue open air is plentiful on the meandering highways and in the campgrounds where many bikers stay, but contact tracers last year reported 649 virus cases from every corner of the country linked to the rally, including one death.

A team from the US Centres for Disease Control and Prevention concluded in a published study that the 2020 rally “had many characteristics of a superspreading event”.

Rallygoers reasoned that after years of riding Harleys, the coronavirus was just another risk. Five motorcycle riders were killed in crashes during the 2020 rally, and one fatal crash has already been reported this year. The attitude was summed up on a T-shirt sold last year: “Screw COVID. I went to Sturgis.”

While it’s not clear how many cases can be blamed on last year’s rally, it coincided with the start of a sharp increase across the Great Plains that ultimately crescendoed in a deadly winter. The gathering could potentially power a fresh wave of infections like the one that is currently shattering hospital admission records in parts of the US South, said Dr Michael Osterholm, the director of the University of Minnesota’s Centre for Infectious Disease Research and Policy.

“I understand how people want to move on from this pandemic – God knows I want to – but the reality is you can’t ignore it,” he said. “You can’t just tell the virus you’re done with it.”

The current rate of cases in South Dakota is roughly half of what it was in the days leading up to last year’s rally. Deaths have also dropped significantly.

The biggest step the city has taken was to allow rallygoers to drink on public property, reasoning it will spread the bacchanalia into the open air.

Only about 46 per cent of adults in the county that hosts Sturgis are fully vaccinated, according to the CDC, compared with 60.6 per cent nationwide. Vaccination rates were similarly low in the five counties where most 2020 rallygoers hailed from, according to an analysis of cellphone data from the Centre for New Data.

Vari, the biker from Hungary, said he’s been fully vaccinated – but only because he falsely thought he needed proof of vaccination to get into the US.

“Sturgis or bust,” he wrote on Facebook.