CAPE TOWN, South Africa — For students around the world, 2020 has been a year of lost progress and pent-up energy. For high school seniors in South Africa, whose final term is ending well before vaccine rollouts, that feeling has been particularly acute: no formal dances, no graduation ceremonies — no fun.

But in a beach town last week, more than 3,000 17- and 18-year-olds went ahead with a huge, week-long graduation party, and more than 1,000 of them have since tested positive for the coronavirus. Hundreds more refused to get tested or gave wrong numbers to contact tracers.

Then, on Friday evening, South Africa’s health minister announced that researchers had discovered a new strain — similar to one found in Britain this week — that he said seemed to affect young people more than strains that had previously been circulating.

“Clinicians have been providing anecdotal evidence of a shift in the clinical epidemiological picture — in particular noting that they are seeing a larger proportion of younger patients with no co-morbidities presenting with critical illness,” said the minister, Zweli Mkhize. The evidence “strongly suggests that the current second wave we are experiencing is being driven by this new variant.”

While Mkhize did not draw a connection between the party, which other officials have termed a “superspreader” event, and the proliferation of the new strain, their combined effect has been a surge in cases and hospitalizations across three provinces in Africa’s hardest-hit country.

“Our youths are not wearing masks,” with some “clearly intoxicated,” he said, referring to graduation revelries. “They’re throwing away caution to the wind and don’t care about the rules of the disaster.”

It was unclear whether the sudden spike would result in travel restrictions, after South Africa had recently relaxed limits, but Mkhize said Wednesday that cases were “growing exponentially” and warned that additional restrictions would probably be necessary. Many at the beach party had traveled between provinces to attend.

“We knew in the back of our minds that covid is going to spread at the parties, but a lot of people are sentimental about the matric year,” said Zak Baitz, 18, referring to the final year of high school. He attended the party with five of his friends, all of whom had the blessing of their parents. “A lot of us were saddened by how this year ended up for matrics.”

President Cyril Ramaphosa cited the party as a “harsh reminder” about irresponsible behavior while announcing the reimposition this week of a curfew, targeted lockdowns, limits on alcohol sales and the closures of most beaches and public parks. The holiday season coincides with summer in South Africa.

“The sad truth about this pandemic is that festivals, concerts and parties — which should be occasions for fun and joy — are proving to be sources of infection and illness, and may even lead to deaths,” Ramaphosa said. “Unless we do things differently, this will be the last Christmas for many, many South Africans.”

Around the world, from South Dakota to Singapore, superspreader events have fueled dramatic rises in cases well beyond the vicinity of their origin. Early outbreaks that made South Africa the center of the spread of the coronavirus in Africa were caused by superspreader events in Cape Town.

“The beginnings of South Africa’s second wave may have predated the recent parties, but they served to amplify the spread of the virus at a critical time so that it created widespread community transmission,” said Salim Abdool Karim, co-chair of South Africa’s coronavirus task force. He noted that other events at nightclubs and universities attended by young people were also to blame.

On Wednesday, South Africa recorded more than 10,000 new cases, with more than 1 in 5 of those tested returning a positive result — a sign that many more cases are going unrecorded.

South Africa had initially imposed one of the strictest lockdowns in the world, with bans on sales of cigarettes and alcohol, nearly all travel restricted, restaurants and bars closed. Even walking the dog could result in a ticket. By November, the country was registering only around 2,000 cases a day.

More than 24,000 have died of covid-19 in South Africa, accounting for nearly 40 percent of all coronavirus-related deaths in Africa. Experts attribute the higher death rate compared with the rest of the continent to a higher proportion of the population being over the age of 65 and thus more at risk of severe complications.

Party organizers initially protested the superspreader label, saying it was irresponsible to use it without statistical proof and denying reports that dozens of attendees tested positive. Officials from the province that includes the cities of Johannesburg and Pretoria, where many of the attendees ­originated, then published party-
specific numbers.

“These students had 340 contacts of which 32 tested positive,” their report said, adding that most of the new cases in the province were among 11- to 20-year-olds.

Graduation parties — known here as “rage festivals” — have been postponed in other parts of the country after public outrage and warnings by health authorities that such gatherings were adding to the new wave of infections.

The largest increase in new cases has been in Cape Town and surrounding wine lands, where the country’s first coronavirus cases emerged in March. KwaZulu-Natal province around Durban and the Johannesburg metro area are the second- and third-most affected.

“Our beaches are known for overcrowding during this time, and people tend to be carefree,” Mkhize said earlier this week, warning that those heading to beaches that remain open need to “ensure that it does not become a day of regret where people get infected and lives are lost.”

Baitz said that precautions were taken at the rage festival he attended outside Durban and that the party was smaller than in previous years. Some partygoers were tested beforehand, and everyone was encouraged to wear masks. In the end, though, it was a rollicking party, and social distancing was impossible.

A day before the week-long festival ended, Baitz developed a cough and lost his sense of taste and smell, he said.

“We knew the consequences and the possibilities,” Baitz said. “A lot of people weren’t worried about getting sick.”

Bearak reported from Nairobi.