It wasn’t long ago that President Donald Trump and other Republicans were diagnosed with the coronavirus that people have detected as a common thread: they had all been to the White House on September 26.
Numerous people who attended the event to announce Amy Coney Barrett’s appointment to the Supreme Court are known to have contracted 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 collection.
The emerging White House cluster is the type of incident infectious disease experts are focusing on as a crucial way to understand how coronavirus spreads. They are known as “superspreader”
“What triggers the transmission is based on multiple factors and you get the best and biggest super diffusion events when all the stars align the wrong way,” said Jamie Lloyd-Smith, professor of ecology and evolutionary biology at the ‘UCLA.
As the pandemic has evolved, infectious disease experts have focused on so-called super diffusers which are believed to play an important and disproportionate role in transmitting the virus.
While the 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 which public health strategies will be most effective in curbing runaway epidemics.
There is no official definition for superspreader events, but they are characterized by incidents that result in a large group of infections. In March, a Biogen corporate meeting in Boston is thought to have been linked to 20,000 cases of Covid-19, according to a study published on the medRxiv prepress server that has yet to be peer reviewed. In Michigan, a group of over 180 cases was tracked down to a restaurant and bar in East Lansing in June. And an indoor wedding in Maine in August is thought to have resulted in at least 176 coronavirus cases and seven deaths.
Those incidents and others suggest that although any infected person can spread the virus, there are circumstances in which transmissions can get out of control.
One of the main factors is the setting. The virus can be spread through airborne transmission, which means it can persist in tiny droplets in the air. This makes some environments particularly risky, Lloyd-Smith said.
“A perfect storm is someone who is spreading a lot of virus in a space where they are able to share that virus effectively, then an interior space without much ventilation with a lot of other people – and particularly if those people are not consistent with practices. like wearing masks, “he said.
But there are also many individual variations and it is unclear whether an infected person, given the right environmental factors, could become a super speaker.
“I don’t think we can tell whether it’s due to the individual or just the event,” said Seema Lakdawala, assistant professor of microbiology and molecular genetics at the University of Pittsburgh School of Medicine. “I would say they are both very important.”
An infected person’s viral load – or the amount of virus that is actually in their body – is thought to play an important role, but it’s not clear how.
“It’s nearly impossible to trace the real traits on an individual level in these super diffusion events because you don’t know they’re happening when they’re happening,” Lloyd-Smith said. “We can’t go back in time and swab our nose for a sample at that critical moment of the broadcast.”
Another challenging aspect is that people infected with the virus can spread it before they experience any symptoms, meaning some super speakers may exhibit others without knowing they are infected, Lakdawala said.
Also, it’s not known if there are any biological differences that make the virus more stable in some people’s mucus, Lakdawala said. If so, it could mean that super speakers are only more effective at transmitting the pathogen when they cough, sneeze, or speak.
Lakdawala’s lab is studying some of these ideas, including whether exposure of some people to other viruses and bacteria gives them unique super-spreading characteristics, but said it’s too early to know.
While scientists are working to understand what factors are most important in creating superspreader events, there is mounting evidence that they are driving most of the spread of the virus.
A study by researchers from the London School of Hygiene and Tropical Medicine found that around 10% of infected people can be responsible for around 80% of the spread of the virus. The findings, published in April on the Wellcome Open Research platform, were supported by similar research, including a recent study of 85,000 coronavirus cases in India. The research, published in the journal Science on September 30, found that about 5 percent of people studied accounted for 80 percent of new infections detected through contact tracing.
“It is really becoming clear that the way this virus spreads is very erratic,” Lloyd-Smith said. “There is a minority of people who end up doing most of the broadcast.”
These findings have important implications for public health officials, said Dr Akira Endo, an infectious disease epidemiologist at the London School of Hygiene & Tropical Medicine.
“These outbreaks are unpredictable,” said Endo, author of the study published in Wellcome Open Research in April. “We should focus on limiting the risk of super diffusion events, because we can control some of the environmental and behavioral factors that cause them.”
One way is to limit being in environments where coronavirus is known to spread easily, Lloyd-Smith said.
“The measures you take to prevent daily transmission are similar to the measures you would take to prevent super-spread events,” he said. “We need good compliance with basic measures we’ve been hearing about for months now – things like wearing a mask, not spending time around the house and with a lot of people.”