It wasn’t long after President Donald Trump and other Republicans were diagnosed with the coronavirus that people detected a common thread: All of them had been at the White House on Sept. 26.
Numerous people who attended the event to announce the nomination of Amy Coney Barrett to the Supreme Court are known to have caught the virus. Others close to people who tested positive at the event have since also caught the virus, some of whom initially tested negative for several days after the gathering.
The emerging White House cluster is the kind of incident that infectious disease experts are focusing on as a crucial way to understand how the coronavirus spreads. They’re known as “superspreader” events.
“What gives rise to transmission is based on multiple factors, and you get the best and biggest superspreading events when all the stars align in the wrong way,” said Jamie Lloyd-Smith, a professor of ecology and evolutionary biology at UCLA.
As the pandemic has evolved, infectious disease experts have zeroed in on so-called superspreaders who are thought to play a major and disproportionate role in transmitting the virus.
Although pieces of the puzzle are still missing, understanding those broader patterns of transmission will help scientists pinpoint not only how the virus spreads, but also what public health strategies will be most effective to curb runaway outbreaks.
There is no official definition for superspreader events, but they are characterized by incidents that result in a large cluster of infections. In March, a Biogen corporate meeting in Boston is thought to have been linked to 20,000 Covid-19 cases, according to a study published to the preprint server medRxiv that has yet to be peer-reviewed. In Michigan, a cluster of more than 180 cases in June was traced to a restaurant and bar in East Lansing. And an indoor wedding in Maine in August is thought to have resulted in at least 176 coronavirus cases and seven deaths.
Those episodes and others suggest that although any infected person can spread the virus, there are circumstances in which transmissions can spiral out of control.
One major factor is the setting. The virus can be spread through airborne transmission, which means it can linger in tiny droplets in the air. That makes certain environments particularly risky, Lloyd-Smith said.
Video: The typical progression of Covid-19 virus (CNBC)
“A perfect storm is someone who is shedding a lot of virus in a space where they are able to share that virus effectively, so an indoor space without much ventilation with a lot of other people — and particularly if those people are inconsistent with practices like wearing masks,” he said.
But there’s also a lot of individual variation, and it’s not clear whether any infected person — given the right environmental factors — could become a superspreader.