Coronavirus spread much faster in China than earlier thought with 1 person infecting 5 others, new data shows
When the coronavirus outbreak took hold in China, the virus moved fast, jumping from one person to at least five others, allowing it to spread far and wide. This means the virus circulated at a rate faster than previously assumed.
Revisiting data from China during the early stages of the outbreak, researchers presented fresh estimates in their Centers for Disease Control and Prevention (CDC) report. In it, they found that an infected person may have passed on the virus to an average of 5.7 other people. This makes it hard to stop the virus from spreading.
Every time a new virus attacks, scientists try to find out how many people can catch the virus from a single infected person. This measure is called the Reproduction number or R naught (R0). Earlier, scientists thought, 2 to 3 people, on average, were contracting the infection from a single person.
To arrive at the estimate, the team collected two sets of data: domestic travel and coronavirus cases -- including data on when people reported symptoms and their hospitalization records -- in provinces other than Hubei, which was then the epicenter of the outbreak.
The team then combined the two sets of data to arrive at the estimate of 5.7. According to them, to stop the virus more than 82% of the population has to be immune to it. There are two ways of achieving immunity: vaccination or prior infection. It could take at least 18 months for an effective and safe vaccine to reach the markets. And researchers are trying to figure out whether the virus can strike people more than once.
In the absence of a vaccine or knowledge of whether the virus can reinfect patients, the researchers call for strict measures. "We further show that active surveillance, contact tracing, quarantine, and early strong social distancing efforts are needed to stop transmission of the virus," the team wrote in their report.
The report adds that measures such as contact tracing and quarantining can bring down the spread, provided there are not many unidentified infected patients. These people do not see a doctor because they either show mild or no symptoms and are hence not documented in records. But, the report adds, if unidentified infected persons drive 20% of the spread, countries will need stricter measures like high levels of social distancing efforts to stem the spread.
An earlier study predicted that unidentified infected persons were driving the outbreak in the early stages. "The explosion of COVID-19 cases in China was largely driven by individuals with mild, limited, or no symptoms who went undetected," says co-author Dr. Jeffrey Shaman, professor of environmental health sciences at Columbia University Mailman School.