COVID-19 superspreading events play bigger role in disease spread than previously thought, claims study

Over 47 million people have tested positive for the COVID-19 infection in the world so far. Of these, more than 34 million have recovered and over 1.2 million have died.

The virus spreads through droplet transmission when an infected person coughs, talks or sneezes. As per the current data, the basic reproduction number of COVID-19 is about three. This means, one infected person can infect three people on an average. However, the transmission of this disease is not so simple.

Many people do not spread the disease at all. On the other hand, several superspreading events have been reported during the pandemic wherein one infected person was seen to infect a lot more than three healthy people. Still, scientists didn’t know exactly how much of a role superspreading events play in the overall spread of disease.

Now, a group of researchers at MIT claim that superspreading events have a much larger impact on the transmission of SARS-CoV-2 than was assumed or expected.

The findings of the study are published in the Proceedings of the National Academy of Sciences of the United States of America.

While studying about 60 superspreading events where a COVID-19 patient infected more than six people, the researchers noted that these events were much more common compared to what is observed through the statistical distributions used in epidemiology.

So, to study the extent of superspreading events and understand the ways to control the outbreak, the researchers used mathematical tools used in finance and insurance models to study fat tail events (those with a tendency to have an extreme deviation from the median) by looking at the superspreading events from the past.

They defined a superspreading event to be one where an infected person passed on the disease to more than six people and, based on this, found a total of 60 superspreading events -- 15 from the SARS outbreak in 2003 and 45 from the COVID-19 outbreak. As per a news release by MIT, during most of these events, between 10 and 100 people were infected. However, in two events, more than 100 people got infected.

On plotting the findings on a graph, the researchers found that superspreading events are extreme but they are still more common than previously anticipated.

Controlling large gathering

The authors of the study pointed out that various factors such as the viral load (amount of virus present in the body) decide if a person is a superspreader. A previous study had also indicated that people who release more droplets while coughing or talking are more likely to spread COVID-19 to more people.

However, these factors were not included in the latest study. Instead, the researchers focussed on how many people an infected person comes in contact with.

To study this, they created and compared two mathematical models. The average number of people coming in contact with every person was 10 in both the models. However, in one of the models, the total number of contacts per person kept on declining exponentially while some people in the other model had come in contact with an increased number of people.

In the second model, more people were found to be infected. However, the number declined significantly when people with more than 10 contacts were taken out of context.

The authors mentioned that if we can reduce the total number of people a person comes in contact with to less than 10, superspreading events can be significantly reduced.

For more information, read our article on Who are superspreaders and how to stop them.

Health articles in Firstpost are written by myUpchar.com, India’s first and biggest resource for verified medical information. At myUpchar, researchers and journalists work with doctors to bring you information on all things health.