SEOUL — These should be the days of the chicken in Seoul.

Following an adage — “Fight the heat with hot food” — South Koreans traditionally gather to eat steaming chicken with rice, ginseng and other medicinal herbs during Boknal, a midsummer period that is supposed to mark the hottest days of the season.

Instead, a sharp rise in coronavirus cases in South Korea has brought new restrictions, including a prohibition on gatherings of three or more people after 6 p.m. in public places.

That has left Seoul stumbling back into semi-lockdown after being considered one of the success stories of the pandemic’s early months, with aggressive contact tracing and one of the world’s lowest mortality rates.

Seoul’s chicken restaurants had expected to help mark this summer with a return to the long lines of past Boknals, days that are sprinkled throughout July and August. But Park Mi-ra went a whole evening last week without a single customer at her Seoul restaurant, Smile Rice Chicken Baeksuk, which specializes in the traditional chicken dishes.

Such restaurants can be found in every neighborhood in the South Korean capital. In the past, dog meat soup was a staple for Boknal festivals, but that tradition has faded.

Seoul is just one scene in a pandemic boomerang playing out around the world as the delta variant causes officials to renew emergency measures and appeals from Bangkok to Rome to Los Angeles.

South Korea’s daily coronavirus caseload peaked at 1,842 on Thursday. The infection numbers are worrying for a country where only about 13 percent of people have been fully vaccinated and about 70 percent are waiting for their first shot.

In Seoul, schools have returned to online classes, nighttime public transit has been cut back and a curfew on restaurants and bars has returned.

Park and her husband opened their restaurant last summer when the city’s daily infections were in single digits.

“Back then, we thought we were done with the virus and figured it was a good time to open the restaurant,” said Park, 49, who is still waiting for her first vaccine dose.

Health experts say South Korea’s government got off to a slow start on vaccinations, believing it could continue to contain the virus through measures such as testing and social distancing.

“We are so sorry about the hardships to the small-business owners caused by the virus measures,” South Korean Prime Minister Kim Boo-kyum said this month as he rolled out the toughest social distancing the country has seen.

Earlier this year, Park and her husband received 2 million won ($1,750) in coronavirus aid that the government provided to small-business owners — in which she found a “consolation.”

She has kept the restaurant open through the pandemic with a host of anti-virus measures, such as regular disinfection and customer record-keeping in accordance with the government’s contact-tracing mandate.

Park’s restaurant is also making up for lost dine-in customers with delivery orders. Her husband goes to a nearby traditional medicine market in the morning to buy herbs and roots to put into their chicken dish.

“I wish vaccines were made available earlier, but in the meantime, we can have this nutrition-packed chicken soup and wait out this difficult summer,” Park said.

Kim Jae-soo, who operates a chicken restaurant in southern Seoul, has seen the number of customers fall by two-thirds since the new virus curbs. “Eating chicken on Boknal is a ritual for Koreans,” Kim said. “However, even Boknal could not escape the virus.”