COVID-19: who are superspreaders and how to stop them?

Superspreading events (SSE) are not limited to infectious diseases that have emerged recently. According to the United States' Center for Disease Control and Prevention, an asymptomatic carrier of typhoid went on to infect 50 people in the early 20th century. 

Researchers thereafter arrived at a 20/80 rule, suggesting that about one in five people are responsible for 80% of all new infections. This empirical rule, according to research, explains the spread of diseases—those who end up spreading the infection at an abnormally higher rate are known as superspreaders.

There are several theories about what makes a person a superspreader, but there isn't any conclusive evidence to explain it yet. It is thought to have some link with the immune system of the person, as superspreaders tend to be highly infectious despite being asymptomatic—they don't have any symptoms, so they often do not realise that they could be transmitting the infection to others.

Some theories also suggest it could have something to do with the viral load on a person who has been infected, but the general overview is that it is virtually impossible to identify a superspreader before such an event has taken place.

While it is next to impossible to identify a superspreader—even for an infectious disease like COVID-19—unless a superspreading event occurs, researchers at Copenhagen University and Roskilde University have now created a model to analyse superspreading events to come up with counter-measures in various settings, including homes, workplaces as well as other public spaces.

The model, however, requires the use of intensive care units (ICU) of hospitals to be able to measure the impact of the outbreak, as each infected person is allowed to infect another person over a period of time to be able to study the growth rate of the virus, which is calculated with an R0 figure of 2.9.

This study is aimed at identifying clusters and any patterns in the spread of the infection among a certain population. It argues that based on this model, superspreaders can be identified as coming in contact with others at a pre-decided time interval. Reducing the number of people a superspreader comes into contact with by 75% can halt the epidemic. Of course, this requires identifying superspreaders and restricting their movements.

The findings also delve deeper, as separate lockdown events in different social settings can restrict the spread of the disease. For instance, if social contact is restricted or avoided at home, the peak of the epidemic drops by a third, while at a workplace, such restrictions can reduce the peak by half.

According to the findings of the study, random social contacts in public transport, public gatherings or frequent trips to the market, bars or restaurants "is what drives the epidemic". 

According to the researchers, "Superspreaders matter greatly in a mitigation scenario. Epidemics driven by superspreaders are less sensitive to reductions in close contacts at home or work/school, but highly affected by changes in their random contacts."