SARS-CoV-2 transmission: how important is “super diffusion”?


A new study suggests that COVID-19 super spread events are more common than originally believed. Limiting meetings to 10 or fewer people could help prevent this problem.

Scientists have spent most of the past year trying to make sense of the novel coronavirus, SARS-CoV-2, which causes the disease responsible for the ongoing pandemic.

As COVID-19 cases approach 49 million worldwide, researchers continue to study how the virus spreads in an effort to find ways to reduce transmission.

A new study by researchers at the Massachusetts Institute of Technology (MIT), in Cambridge, examines the spread of COVID-19 in large gatherings. It shows that super spread events are more common and have a greater impact on the overall spread of the virus than previously thought.

In their study paper, published in Proceedings of the National Academy of Sciences, thethe researchers explain that these events play an “outsized” role in the transmission of the virus.

On average, SARS-CoV-2 spreads from one person to two or three others. In some cases, the virus is not transmitted. But it can pass to dozens of other people in a relatively short period.

A super spread event is an encounter in which the virus is passed from one person to many others. The researchers behind the present study believed that the super-spread occurs when at least six people acquired the virus.

One such event, a choral practice, took place in Skagit County, WA. Scientists tracked 53 COVID-19 cases to a person with a SARS-CoV-2 infection during trials.

Of the 61 people who attended the 2.5-hour event, 33 tested positive for COVID-19 and another 20 had probable cases.

Since COVID-19 mainly transmits through respiratory droplets, choir practice was a privileged environment for its spread.

Some other COVID-19 super spread events include the White House Rose Garden event where 35 out of about 200 attendees acquired the virus and a birthday party in Westport, CT, where 20 of the 50 party attendees acquired the virus. virus.

Researchers at MIT studied data from 60 super spread events, including some from the ongoing COVID-19 outbreak and others from the 2003 SARS outbreak.

To determine the impact of these events on overall virus transmission, the researchers created two mathematical models.

When they plotted the data, using statistical tools, they found that the transmission distribution had a “fat tail”.

“This means that the likelihood of extreme events decays more slowly than would have been expected,” said study lead author Felix Wong, a postdoctoral fellow at MIT.

“These really large super spread events, with between 10 and 100 people infected, are much more common than we anticipated,” he added.

As the likelihood of extreme transmission events decreases slower than expected, there is a high likelihood of COVID-19 being spread in large gatherings.

“Super diffusion events are probably more important than most of us initially thought. Even if they are extreme events, they are probable and therefore probably occur with a higher frequency than we thought. If we can control super spread events, we have a much better chance of keeping this pandemic under control. “

– senior author James Collins, the Termeer Professor of Medical Engineering and Science at MIT

Many public health officials have recommended limiting the number of people to meetings from the early stages of the pandemic.

Having more people at an event increases the likelihood that at least one person present has COVID-19 and that the underlying virus is spreading to more people.

However, there hasn’t been a consistent agreement on what constitutes a large gathering.

While the actual frequency and impact of these super dissemination events may be worrying, the findings can help public health officials develop consistent recommendations.

“It gives us guidance on how we can control the ongoing pandemic, which is by identifying strategies that target super-speakers,” says Wong.

“One way to do this would, for example, be to prevent anyone from interacting with more than 10 people in a large meeting,” he suggests.

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