Over the past three months, the novel coronavirus has spread to over 192 countries and has infected more than three lakh people.

The rate at which an epidemic spreads depends on two factors – how many people each person infects, and how long it takes for an infection to spread between people. The first quantity is called the reproduction number; the second is the serial interval.

A study has found that more than 10 percent of people who get infected with the novel coronavirus are infected by people who do not exhibit symptoms but are infected. They were also able to calculate the serial interval of the virus.

To measure this 'serial interval', scientists looked at the time it takes for symptoms to appear in two people with the virus: the person who infects another, and the infected second person. The short serial interval of COVID-19 means emerging outbreaks will grow quickly and could be difficult to stop, the researchers said in a statement.

A team of researchers comprising of scientists from the United States, France, China and Hong Kong found that the average serial interval for the virus was around four days.

“Ebola, with a serial interval of several weeks, is much easier to contain than influenza, with a serial interval of only a few days. Public health responders to Ebola outbreaks have much more time to identify and isolate cases before they infect others,” said Lauren Ancel Meyers, a professor at the University of Texas in a statement. “The data suggest that this coronavirus may spread like the flu. That means we need to move quickly and aggressively to curb the emerging threat.”

The process

The team looked at 450 infection case reports from 93 cities in China. They found that more than one in 10 infections were from people who had the virus but did not yet feel sick which is known as pre-symptomatic transmission.

This study could help in medical experts and other health officials can use this evidence to stop this particular type of transmission of Covid-19.

“This provides evidence that extensive control measures including isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings may be warranted,” Meyers said in a statement“Asymptomatic transmission definitely makes containment more difficult.”

Previously, scientists were doubtful about the spread of COVID-19 via this method. However, this study offers proof that people who do not show the symptoms could be carriers and can still spread the disease. The findings from this study is published in the journal Emerging Infectious Diseases.

What are the different stages of the spread of the virus?

Stage 1 - Imported cases
These cases are the people who have travelled to foreign countries; places that have confirmed cases of the virus and have come back to India.

Stage 2 - Local transmission
Like mentioned above, these cases are those people who have come in contact with those that have a travel history.

Stage 3 - Community transmission
This is the stage we need to avoid as there is no way that the virus can be traced back to a certain person.

Stage 4 - Epidemic
This is the last stage and what the world saw China grapple with.