Coronavirus pandemic: Infected people without symptoms may be behind COVID-19's rapid spread, finds study
About 86% of people infected early in the outbreak might have escaped detection in China. The virus moved discreetly in the beginning stages, explaining why it spread so fast, say experts
The new coronavirus moved undetected in China during the early stages of the outbreak, helping it spread far and wide, according to findings in a new study.
About 86% of people infected early in the outbreak might have escaped detection. "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.
What is more, about two-thirds of people with confirmed infections contracted the disease from those who escaped detection.
"We find for COVID-19 in China, these undetected infected individuals are numerous and contagious. These stealth transmissions will continue to present a major challenge to the containment of this outbreak going forward," adds Dr Shaman.
However, countries might be able to turn this around by taking aggressive actions. China's actions such as travel restrictions may have worked. Further, increased awareness and implementing personal protective measures may have helped slow the spread, says the study.
Another study traced a cluster of infections in Massachusetts to people who were not yet showing symptoms. Other studies have also supported the idea that people with no or mild symptoms seem to be driving the disease spread.
Shaman and his colleagues based their predictions on mathematical modeling. The study included data on reported infection and spread within China along with information on people's movement before and after travel restrictions took force.
We predicted that 86% of people who were infected were undocumented before the implementation of travel restrictions and other control measures, say authors of the study.
These people appear to be driving the infection and facilitating its spread. "The undocumented infections which tend to be milder are distributing the virus broadly. They are contributing essentially to what we call self transmission of the virus because it is undetected and it is flying below the radar," explains Dr Shaman during a teleconference.
The study raises the possibility of the virus setting down. Control measures, though successful in reducing the spread, may not stop the virus. "It is unclear whether this reduction will be sufficient to fully stem the virus spread. If the novel coronavirus follows the pattern of 2009 H1N1 pandemic influenza, it will also spread globally and become a fifth endemic coronavirus within the human population," says Shaman.
The study has been published in Science.