India — In Uttarakhand’s Haridwar, thousands of devotees gathered to take a dip in the Ganges on the thirteenth day of the Mahakumbh on Wednesday, even as India continues to battle an intense second wave of Covid-19 infections.
Whether it’s a religious event or a conference or a rally, super-spreading events that can infect dozens, hundreds, even thousands, of people have illustrated the potential for the coronavirus to infect in dramatic bursts. Such events have grabbed headlines, looming large in the narrative of the unfolding pandemic.
Experts say these large clusters are more than just extreme outliers, but rather the pandemic’s likely main engine of transmission. This corresponds to the 80/20 rule of epidemiology, where 80% of cases come from only 20% of those infected. Benjamin Althouse, research scientist at the University of Washington’s Institute for Disease Modeling, said that coronavirus may be even more extreme, with 90% of cases coming from potentially just 10% of carriers.
Here are some of the biggest super-spreader events globally.
1. Mulhouse, France
Beginning February 18, 2020, Christian Open Door church in Mulhouse, a city of 100,000 on France’s borders with Germany and Switzerland, hosted a week-long annual celebration. Thousands flocked to the event from across the globe. At the time, France had 12 confirmed cases, according to World Health Organization (WHO) data.
There were none in the Mulhouse area. The prayer meeting kicked off the biggest cluster of Covid-19 in France to date, local government said. Around 2,500 confirmed cases have been linked to it. Worshippers at the church unwittingly took the disease caused by the virus home – to the West African state of Burkina Faso, the Mediterranean island of Corsica, to Guyana in Latin America, to Switzerland, and even to a French nuclear nuclear power plant.
Antoinette, one of the attendees, on March 4, became one of the first cases of Covid-19 on the French island of Corsica. By March 20, France had more than 10,000 cases of Covid-19. Around a quarter were in Grand-Est, the region that includes Mulhouse. “The very great majority” of these could be traced to the church, said Michel Vernay, the local public health official.
2. San Siro, Italy
It was the biggest soccer game in Atalanta’s history and a third of Bergamo’s population made the short trip to Milan’s famed San Siro Stadium. Nearly 2,500 fans of visiting Spanish club Valencia also traveled to that Champions League match. In total, 44,236 people were present at the stadium.
More than a month later, experts began pointing to the February 19 game as one of the biggest reasons why Bergamo has become one of the epicentres of the coronavirus pandemic – a “biological bomb” was the way one respiratory specialist put it – and why 35% of Valencia’s team became infected.
The match, which local media have dubbed “Game Zero”, was held two days before the first case of locally transmitted Covid-19 was confirmed in Italy. Nearly 7,000 people in the province of Bergamo had tested positive for Covid-19 and more than 1,000 people had died from the virus – making Bergamo the most deadly province in all of Italy for the pandemic. The Valencia region reported more than 2,600 people infected.
3. Kuala Lampur, Malaysia
An Islamic missionary movement Tablighi Jama’at gathering held between February 27-March 1 last year at a sprawling mosque complex on the outskirts of Malaysia’s capital Kuala Lumpur emerged as a source of hundreds of new coronavirus infections spanning Southeast Asia.
It was attended by 16,000 people, including 1,500 foreigners. Out of Malaysia’s 673 confirmed coronavirus cases, nearly two-thirds are linked to the four-day meeting, Malaysia’s minister of health Adham Baba said. It is not clear who brought the virus there in the first place.
The packed gathering, where guests had to take shuttle buses to sleep at other venues, was attended by nationals from dozens of countries, including Canada, Nigeria, China, South Korea, India and Australia, according to an attendee list posted on social media. Brunei has confirmed at least 50 cases linked to the mosque gathering. Singapore announced five linked to the event, Cambodia 13 and Thailand at least two.
4. Daegu, South Korea
Other religious gatherings have been linked to the spread of the virus: A large church in South Korea triggered the largest cluster of cases outside of Wuhan, China, where the virus was first discovered in February last year.
In early February, South Korea’s coronavirus outbreak appeared to be contained as the number of confirmed infections stabilised at 30. Then, on February 17, a 31st case surfaced at a health clinic in Daegu, a city about 150 miles south of the capital where the vast majority of known infections were located. An unidentified 61-year-old woman, who lived there and occasionally commuted to Seoul, tested positive for the virus.
It seemed like a standard case until public health authorities started tracing the patient’s tracks. What they learned shocked them – the woman had, during the previous 10 days, attended two worship services with at least 1,000 other members of her secretive religious sect.
Within 24 hours, the nation’s number of confirmed cases started multiplying exponentially. The tally rose by 20 during that period, doubled the following day and then doubled again on the third day.
By February 26, the count skyrocketed past 1,000 – a more than 30-fold increase in a week that prompted the government to raise its health alert to the highest level. At least half of the new cases are linked to the sect called the Shincheonji – which translates to “new heaven and land” and whose members worship side-by-side in cramped spaces. More than 5,000 cases have now been attributed this religious ceremony.
5. Washington DC, US
As the world looked on shocked by the events of January 6, when hundreds of unmasked supporters of former US president Donald Trump stormed the Capitol building in order to stop the certification of Joe Biden as the winner of the 2020 elections, a super-spreader event may have been in the making.
In the days after the deadly riot, the former director of the Center for Disease Control and Prevention, Dr Robert Redfield called it a “surge event”.
“These (unmasked) individuals all are going in cars and trains and planes going home all across the country right now. So, I do think this is an event that will probably lead to a significant spreading event,” Redfield told McClatchy in an interview.
In a working paper, yet to be peer-reviewed, economists at San Diego State and Bentley universities suggest that the riot “may have led to non-localized community-level Covid-19 spread”, meaning that the protesters, who came from all over the country, returned to their homes states after the even, resulting in the spread in their own communities instead of in their direct vicinity as usually the case in such super spreader events.
Having said that, 150 National Guard troops, 38 US Capitol Police officers and at least four members of Congress tested positive after the siege in Washington DC.
“All the cases to likely derive from this event will likely be lost in the huge number of cases we have in the country right now,” Eric Toner, senior scholar at the John Hopkins Center for Health Security, had told the Washington Post in its aftermath.
This was not the only event linked to Trump, and his coronavirus denial and mismanagement. Stanford University economists estimate that Trump’s campaign rallies ahead of the November 3 elections resulted in 30,000 additional confirmed cases of Covid-19, and likely led to more than 700 deaths overall.
The research, led by B. Douglas Bernheim, chair of economics at Stanford University, analysed data following 18 Trump rallies held between June 20 and September 22, three of which were indoors. Bernheim said in an email the work relies on statistical methods to infer causation after an event has occurred.
6. Boston, US
An international conference hosted by the Biogen, an American biotechnology company, in Boston’s Marriott Long Wharf hotel resulted in over 300,000 cases, according to a study published in the journal Science.
At least 99 Covid-19 cases were reported from the event that occurred between February 26 and 27 of last year in March. Sequencing the genomes of the virus obtained in March revealed two mutations that had not been reported before in the US prior to the conference.
The first variant of the virus infected around 245,000 people the US, while the second infected 88,000 cases. The conference was responsible for around 20,000 cases in the Boston area alone. A “highly similar viruses within a narrow time window,” indicating a super-spreader event, the researchers wrote in the Science article.
7. Sturgis, US
In early September, several US Midwestern states experienced rising numbers of Covid-19 cases, many seemingly linked to an annual motorcycle rally in Sturgis, South Dakota.
The rally, held from August 7 to 16, drew an estimated 460,000 motorcycle enthusiasts. Bikers crowded into bars and rock shows, mostly ignoring social distancing recommendations. Few wore masks. As a result, the rally was linked to hundreds of coronavirus cases across more than 10 US states.
A study published by the IZA Institute of Labor Economics that used cell phone data to track movements claims that 266,796 cases between August 2 and September 2 can be linked to the Sturgis rally – 19% of the 1.4 million national coronavirus cases during that time period.
However, this number is heavily disputed: South Dakota state epidemiologist Josh Clayton criticised the study for not accounting for the fact that cases had already been on the rise, which could partially be attributed to school reopenings. Johns Hopkins university said “data analyses used to obtain nationwide estimates were relatively weak”.