A recent outbreak of Covid-19 cases among officials in Washington, with dozens testing positive after attending the Gridiron Club Dinner, has put the concept of Covid-19 superspreading back in the spotlight.
Covid-19 superspreading, which involves the virus spreading at a single event on a larger scale than what is typically expected, is still possible and poses a risk. But in this stage of the pandemic, a large event may not necessarily be an invitation to widespread, unchecked illness – if people use tools now available to limit risk, according to public health experts.
Now, there are more tools to curb the spread of Covid-19: authorized vaccinations that limit illnesses and infections, robust supplies of at-home tests that can indicate whether someone needs to isolate, face masks to wear in high-risk situations and therapeutics that can reduce severe disease.
“We used to be concerned because these superspreading events would put a lot of people in the hospital and as a consequence, some in intensive care units, and even some people dying. This is less likely to happen now,” said Dr. William Schaffner, a professor in the Division of Infectious Diseases at Vanderbilt University Medical Center. “Given the level of natural immunity as well as vaccination in our communities, most people infected now are going to get mild illness that doesn’t require them to be hospitalized.”
Meanwhile, it’s also more complicated to pin Covid-19 cases to specific events. Contact tracing has virtually disappeared, and people can encounter Covid-19 in any number of circumstances as workplaces, shops and restaurants reopen and masks come off.
But by using the right tools at the right times, there are hopes that Covid-19 superspreading could become a thing of the past.
‘The pandemic isn’t over’
Earlier in the Covid-19 pandemic, superspreading at business conferences, political events and even choir practice helped shape understanding of just how transmissible the coronavirus could be.
In one case, a biotech conference was attended by 200 people in late February 2020 and may have been connected to about 20,000 Covid-19 cases in the Boston area, according to research from the Broad Institute of MIT, Harvard University and other institutions.
A report published by the US Centers for Disease Control and Prevention in May 2020 described how a symptomatic person with Covid-19 attended a choir practice in Washington state. Afterward, about 87% of the other choir members developed Covid-19.
But those superspreading events happened before it was exactly clear how the virus spread and who was most at risk, and long before Covid-19 vaccines were made available in December 2020.
“The pandemic isn’t over. We’re still going to see cases of this virus spreading, and we have to continue to be vigilant. We have to continue to be careful,” Dr. Ashish Jha, the White House’s new coronavirus response coordinator, said on ABC’s “Good Morning America” on Monday.
Jha said he is not aware of anyone getting severely ill after the Gridiron dinner in Washington. “As long as people are vaccinated and boosted, we now have a lot of treatments available, put that together, and the good news is, no one out of that so far has gotten particularly sick.
“And that’s what we have to be tracking – making sure that when there are outbreaks, we can take care of people.”
Some infectious disease experts argue that despite greater access to vaccines and testing, Covid-19 superspreading events aren’t over.
“I do think this event in Washington was akin to a superspreading event. It was clearly an event where people were gathered together, and the virus attended and made itself known to a lot of people and infected people,” Schaffner said.
Covid-19 superspreading events are not “a thing of the past,” he said. “So do they still happen? Sure. How important are they? Well, they put a fair number of people out of commission for a while, at least having to isolate at home because they were infected.”
The United States is averaging more than 38,000 new Covid-19 cases per day and about 515 new Covid-19 deaths per day, according to CNN’s analysis of data from the US Centers for Disease Control and Prevention and Johns Hopkins University. The Department of Health and Human Services says there are more than 14,700 people hospitalized with Covid-19.
About 66% of the US population is fully vaccinated.
“Although I don’t think superspreading events will cause surges in hospitalizations, they may continue to augment and accelerate transmission of the virus, causing milder disease in our communities,” Schaffner said.
As we transition to living with Covid-19 long-term, there will be more chances to encounter someone with a mild – but still transmissible – infection through everyday activities like going to school, the office, a neighborhood block party, church, a sporting event or happy hour.
But there are also more chances to identify them.
“We’re much more likely now to find people who are positive but asymptomatic than we were two years ago,” said Dr. Georges Benjamin, executive director of the American Public Health Association. But identifying several cases around the same time at the same place does not necessarily mean all of those people were infected at the same event.
“Is that a superspreading event? Some of them may have gotten infected someplace else before they came together – unless, of course, they test themselves before they go,” Benjamin said.
‘Outbreaks can happen’
The concept of a superspreading event “is not new,” said Keri Althoff, epidemiologist at the Johns Hopkins Bloomberg School of Public Health.
“In history, we identify individuals who were superspreaders,” she said. “For example, Typhoid Mary.”
The world’s understanding of superspreading events dates back to Mary Mallon, commonly known as “Typhoid Mary.” Mallon was born in Ireland in the late 1860s and emigrated to the United States, where she worked in a variety of domestic positions for wealthy households before becoming a cook. Researchers have found that Mallon unknowingly carried the bacterium Salmonella typhi, which causes typhoid fever. As a cook, she spread the illness to others – leading to an outbreak in New York.
“She infected hundreds, if not thousands, of people with typhoid because she carried it in her gallbladder and she worked as a cook. Wherever she went, people would get sick,” said Dr. Preeti Malani, chief health officer in the Division of Infectious Diseases at the University of Michigan in Ann Arbor.
The New York Health Department forced Mallon to quarantine.
“She was exiled for decades because she kept infecting others with typhoid,” Althoff said. “She was asymptomatic.”
Mallon’s case is an example of how pathogens can spread on a far-reaching scale, leading to a superspreading event. But she is also an example of how the term “superspreader” can isolate and stigmatize those carrying pathogens, even unknowingly.
In the case of Typhoid Mary, the term “superspreader” was used to describe a person, whereas more recently, the term is being used to describe an event during which many people are infected, probably from more than one infected person at the event. Many experts call the term problematic when used to blame a person for having an illness.
Althoff thinks the United States is at a point where Covid-19 superspreading events are shifting to a thing of the past as the coronavirus circulates widely in our communities.
Events that result in a larger number of infections that wouldn’t otherwise have happened can be better described as outbreaks, Althoff said, similar to how we see outbreaks of other vaccine-preventable respiratory diseases like measles or flu.
“Very early in the pandemic, when the case numbers were low, we saw and investigated superspreading events, and those investigations provided important information about the virus when we knew very little,” Althoff said. “Large-scale outbreaks continue to provide information about how this variant is interacting with a population that has a much higher level of population immunity now than what we had in the beginning of the pandemic.”
So now, when clusters of cases emerge, “instead of ‘superspreader,’ I think the word ‘outbreak’ is a bit more reasonable,” Althoff said. “Outbreaks can happen whenever we find ourselves in higher-risk settings.”
How Covid-19 spreads now
Though “superspreading” events were seen as drivers of Covid-19 transmission early in the pandemic, they are of “much less concern” now, according to Malani.
“A lot of transmission during the Omicron and BA.2 era has been household contact, where the entire family or your household unit gets infected. But really, what I see – and I emphasize this over and over – is that it is social gatherings that are unmasked,” Malani said.
A big difference between the social gatherings happening now and the weddings, funerals or choir practices during the pandemic’s earlier days is that many people now have some immunity against Covid-19 from getting vaccinated, being infected or both.
Based on information from blood samples, about 95% of Americans 16 and older have antibodies against Covid-19 as of December, the most recent date that data is available, according to estimates from the CDC.
The current Covid-19 vaccines are more effective at preventing severe Covid-19 leading to hospitalization or death, but they also offer some protection against infection in the first place. And “staying up to date with COVID-19 vaccination also means you are less likely to spread the disease to others and increases your protection against new variants of SARS-CoV-2, the virus that causes COVID-19,” according to the CDC.
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“What is happening at this point in the pandemic is that people are able to protect themselves differently,” Malani said, adding that people now can gauge their risk for Covid-19 before attending an event by finding out whether others have been tested or vaccinated.
Many Covid-19 outbreaks still happen in pockets of the United States where there are many unvaccinated people, Benjamin said.
“In those areas of the country, those communities where we still have people unvaccinated and numbers of people unboosted, in those cases, we’re certainly going to see bigger, larger numbers of people who test positive,” he said. Superspreading could be more likely in such communities.
Although superspreading events are no longer as much of a concern now as they were earlier in the pandemic, they “are still going to occur,” Benjamin said. “They’re definitely going to be one of the patterns we’re going to see for some time to come from the disease, as long as we still have a variant out there that’s highly infectious and a variety of people in various stages of immune protection.”