BOSTON - As scientists and public health officials around the world race to understand more about the novel coronavirus, research suggests that much of the virus’s transmission is actually driven by a smaller number of individuals, called “superspreaders.”
Some incidents have been reported in the news as “superspreader events,” in which one person unknowingly goes on to infect a large number of other people.
This includes a funeral in Albany, Georgia and a business conference in Boston, which were later deemed to have played “a notable role in the early U.S. spread of COVID-19,” according to a report by the Centers for Disease Control and Prevention.
Dr. Sarah Fortune, chair of the Department of Immunology and Infectious Diseases at the Harvard T.H. Chan School of Public Health, said there are two ways to think about “superspreaders” and their role in transmitting the virus.
First, the individual superspreader. Second, the superspreader event.
What is an individual “superspreader”?
Scientists following the transmission of the novel coronavirus are looking at a metric called the reproduction number (R), which represents the average number of new cases caused by a single infected person.
For this virus, Fortune says it’s somewhere around 2.5. This means that if you have 10 people, there are going to be about 25 new infections.
It’s still unclear if each of those 10 people are giving rise to 2.5 new cases, or if one person is giving rise to 25 new cases. Experts think it may be somewhere in the middle.
“But a lot of transmission is driven by a very few number of people who are seeding lots and lots of cases,” Fortune said. “And that is a classic sense of what a superspreader person is. One of those people, who when they are infected, gives rise to lots and lots of new cases.”
Studies have indicated that most new coronavirus transmissions, roughly 80%, are caused by less than 20% of the carriers.
People wearing masks are seen crowded together on a subway platform at the Fulton Street Subway Station as the city moves into Phase 3 of re-opening following restrictions imposed to curb the coronavirus pandemic on July 8, 2020 in New York City. (Ph
What makes a COVID-19 patient a “superspreader”?
Fortune said for some people, “the way the infection is happening in them is different, and they became superspreader people because of the biology of their infection.”
It’s also clear that there is a trajectory of the virus, and studies have shown that people tend to have a higher viral load early in the course of their infection — perhaps before symptoms even begin, if at all.
So if someone goes to an indoor event early on in their infection, being potentially more contagious but showing no symptoms, Fortune said this can create the perfect storm of a superspreader event.
What makes a gathering a “superspreader” event?
Several incidents have been pinpointed as superspreader events, including a choir practice at a church in Washington state early in the U.S. outbreak.
In March, 61 members of a choir group met for their weekly practice — which was held nearly two weeks before the state’s stay-at-home order. One attendee felt ill, not knowing what they had, and inadvertently ended up infecting 52 others with COVID-19. Two members of the group later died.
“A superspreading event is the things we recognize from the news. All of these events where people came together and large numbers of people got infected,” Fortune explained.
“It’s clear for that to happen, there needed to be the person who was infected at this sort of high level of infectivity, and then all those people had to be around them in sufficient proximity for a sufficient period of time so that they were able to get infected,” she said.
Disease trackers later identified the choir outbreak as a superspreader event, saying the singers sat 6 to 10 inches apart in different configurations during the 2.5 hour rehearsal.
The attendees had no physical contact, but some snacked on cookies and oranges set out or helped to stack chairs. Investigators theorized that the virus could have spread when exhaled droplets landed on those items or by virus particles released during singing.
In May, family and friends in Texas gathered for a surprise birthday party, with about 25 people in attendance. The host was unknowingly infected with the virus and 18 people later tested positive with COVID-19, including grandparents who were hospitalized.
“The problem with superspreaders and superspreading events is that we don’t have a way of recognizing people who are superspreaders. They’re asymptomatic,” Fortune said.
Because it’s not easy to recognize superspreading people, Fortune said the public must be attuned to potential superspreading events.
“That birthday party is the perfect constellation of that because it’s inside. One of the very easiest things we can do is live our lives outside,” she said. “And then because there is this sense of familiarity, it’s very easy to let that social distance drop, take your mask off when you’re inside with your family. You can understand all of that, except consequences can be tragic and unintentionally tragic for people who have the very best of intentions.”
Is there any good news?
Fortune said there is some good news about superspreaders, too, for us collectively.
“When we try to think about how to mitigate transmission, most people are not getting infected walking through the grocery store. So all of this transient contact that people are very anxious about is not how most of this virus is being spread,” she explained.
Fortune added that if people can identify potential superspreading events where there are lots of people gathered together indoors, letting their guard down, and can avoid those events, “that actually can eliminate a huge amount of transmission and relieve a whole lot of anxiety about going to the grocery store.”
“People need to figure out how to live. We have to sustain this and come up with patterns of behavior that are sustainable yet safe,” Fortune said.
This story was reported from Cincinnati.