Clay Goddard wasn’t religious about wearing a face mask in public, despite being the director of the health department in Springfield, Mo., and the head of the region’s response to the novel coronavirus. He doubted a face covering — even his favorite Kansas City Chiefs-pattern mask — offered much protection.

“You’d probably have better luck stopping the wind,” Goddard said.

Few people wore face masks in Springfield, health officials said. The risk from the virus seemed low, with relatively few cases in the city of 170,000. And just wearing a face mask had become, to some, like carrying a political yard sign — especially in a conservative corner of a state that President Trump, who has refused to wear a mask, won easily in 2016. Republican state lawmakers, too, have made a show of going mask-less.

But then a hair stylist in Springfield was diagnosed with covid-19, the disease caused by the coronavirus, in late May, directly exposing 84 customers who had sat just inches from her face for up to 30 minutes each.

And Goddard would end up changing his thinking about masks.

The result appears to be one of the clearest real-world examples of the ability of masks to slow the spread of the coronavirus. It also highlights the challenges for public health officials around the world who at times have sounded ambivalent about masks as they are still trying to understand the threat from this new virus. Several medical studies have shown support recently for the idea that masks work, but going without a mask for some people can still seem like a badge of honor.

The sick hair stylist had worked eight shifts over nine days at a Great Clips on the city’s main commercial strip, despite showing symptoms, according to health officials.

The next day, a second stylist at the same Great Clips tested positive for the coronavirus. She had worked on 56 clients.

The city faced a potentially huge outbreak, just two weeks after reopening barber shops and salons.

“Alarm bells went off,” Goddard said.

But then there were the face masks.

The only places that local health officials required face masks after reopening began May 4 were personal care shops, such as barber shops, nail salons and tattoo parlors.

At the local Great Clips, a sign alerted customers, “A mask is required to enter the salon.” A columnist for the local newspaper wrote about how he forgot to wear a mask when he visited that Great Clips in the days before the infections were made public and had to return to his car to put one on.

Still, at least 140 people had close contact with the two infected stylists — plus an estimated 200 to 300 more people had been inside the salon, according to Goddard.

“I expected five to 10 new cases,” said Robin Trotman, medical director of infection prevention services at CoxHealth in Springfield, who consults with the local health department.

In the first weeks of the pandemic, many public health officials had dismissed the need for face masks outside of hospitals. They had stressed hand-washing and physical distancing. The ability of surgical masks or homemade cloth masks to stop the spread of the coronavirus was controversial.

Studies are only now starting to catch up with the fast-moving pandemic. A review published June 1 in the journal Lancet and funded by the World Health Organization looked at 172 observational studies and found wearing face masks reduces the risk of coronavirus infection.

Yet the public debate remains heated. In Orange County, Calif., opposition to mandatory masking rules recently led local officials to rescind the order. Last month, Ohio Gov. Mike DeWine reversed his decision to require masks in stores after listening to objections that the government was going too far. Several U.S. airlines this week announced they would begin requiring passengers to wear masks while flying.

In Springfield, the two sick hair stylists wore cloth masks, health officials said. Customers wore a mix of different types of masks. But they had been exposed to the virus at close range.

“We knew it was going to almost be like a lab experiment,” Trotman said.

Goddard had to figure out just how bad it might get.

Goddard already had redirected the 115-person Springfield-Greene County Health Department to focus on the coronavirus. Staff that normally worked on chronic disease prevention and community health programs were now contact tracers. Food inspectors, too, tracked down the movements of sick patients.

Goddard said he upset some local residents because the city’s coronavirus rules were tougher than state guidelines. Reopened restaurants faced stricter occupancy limits for social distancing. Contact sports were still not allowed.

He also used mandatory quarantine orders. Since mid-March, when Springfield recorded its first case of the coronavirus, his agency had placed more than 1,000 people under stay-at-home orders after they got sick or were exposed to the virus, checking in by phone with them twice a day.

“We’re walking a bit of tightrope,” Goddard said of trying to prevent virus spread without significant harm to the economy.

The first stylist tested positive on May 21. Health officials had no problem tracking down her clients because Great Clips uses an electronic reservation system.

The Minneapolis-based company declined requests for comment for this article beyond a short statement that thanked “the health department for their important work during this time.” An attorney for the first hairdresser did not return a call for comment.

Goddard held a news conference to announce the first case, saying he was “frustrated” and “disappointed” because the stylist never should have been at work if she was feeling sick.

He also said the health department would offer virus testing to her 84 customers and seven co-workers. The agency recently developed its own in-house coronavirus test.

The next day, the second stylist tested positive. The health department added 56 clients to the list of potential exposures.

While the two Great Clips cases made international headlines, health officials were also dealing with the potential fallout from other sick people visiting the local Price Cutter, Walmart and Petsway. But none of those exposures were as direct or sustained as what happened at Great Clips.

Despite an offer of free testing, just 46 of the 140 Great Clips customers got tested. All were negative.

“We can’t compel them to test,” Goddard said.

Some people said they were too busy or they didn’t feel sick, he said. But he also suspected that some were afraid to get tested — because a positive result meant they would have to miss work.

Fourteen days after the second hair stylist tested positive, Goddard announced that there appeared to be no new infections from the Great Clips exposures. There had been a slight uptick in cases after Memorial Day, but they did not appear to be connected to the hair salon, Goddard said.

Trotman was excited. He plans to study the incident further and hopes to publish a study of the findings.

“Which mask worked, the hairdresser’s or the client’s? I think the answer is yes, they both worked,” he said. “The system worked. Universal masking worked. It really doesn’t matter which one.”

Emily Gurley, an infectious-disease epidemiologist at the Johns Hopkins Bloomberg School of Public Health, who was not connected to the Great Clips cases, was more cautious.

“The best we know this woman infected one other person in her workplace among many potential contacts. And that’s good news. But it’s a data point,” Gurley said. “It’s encouraging, but that’s not strong evidence.”

But it’s already affecting how masks are viewed in Springfield, the third largest city in Missouri.

The city announced that businesses that couldn’t comply with the Centers for Disease Control and Prevention’s recommended six feet for social distancing could instead allow for three feet between people as long as they were wearing a mask, said Matt Morrow, president of the Springfield Area Chamber of Commerce.

“That’s a direct result from what we learned from the Great Clips experience,” he said.

Morrow said he has noticed more people wearing masks in public in recent days — a change he attributed to the lessons from the Great Clips cases.

And Goddard has gone from “an early skeptic” on face masks to a believer.

Now, he wears his Chiefs mask when he goes to the grocery store or runs errands. Goddard said he has noticed a difference among other people, too, with more people opting to wear face masks.

“It’s still just 50-50,” he said. “But I have seen a change in practice here.”