Posted on March 23, 2020 at 12:00 PM
Infectious disease experts investigating the novel coronavirus were able to identify how rapidly the virus would spread, a consideration that may aid public health officials in their attempts at containment. They found that time between cases in a chain of transmission is less than a week and that more than 10 percent of patients are infected by somebody who has the virus but does not yet have symptoms.
A team of scientists from the United States, France, China and Hong Kong were able to calculate what is considered the serial period of the virus in the paper in press with the journal Emerging Infectious Diseases. To calculate the serial interval, scientists are looking at the time it takes for the signs to occur with the virus in two people: the person who infects another human, and the second person who is infected.
Researchers found around four days to be the average serial interval for the novel coronavirus in China. This is also amongst the first research to predict asymptomatic transmission rate.
The pace of an outbreak depends on two factors— how many people infect each case, and how long it takes to spread infection among people. The first quantity is called the number of reproductions; the second is the interval of series. COVID-19's short serial interval means that emerging outbreaks will grow rapidly, and could be hard to stop, the researchers said.
"Ebola, with a serial interval of several weeks, is much easier to contain than influenza, with a serial period of just a few days. Public health responses to Ebola outbreaks have much more time to identify and classify cases before infecting others," said Lauren Ancel Meyers, an Integrative Biology professor at UT Austin. "The data suggest that this coronavirus will spread like flu, suggesting we need to move quickly and actively to curb the danger that is growing."
Meyers and her team looked at more than 450 case reports of infection from 93 cities in China and found the strongest evidence yet that people without symptoms need to transmit the virus, known as pre-symptomatic transmission. According to the paper, there were more than 1 in 10 illnesses by individuals who had the virus but have not yet felt ill.
Earlier, researchers had some confusion with the coronavirus about asymptomatic transmission. The new evidence could give public health officials advice on how to control the disease's spread.
"This provides evidence that stringent control measures may be needed including segregation, lockout, school closures, travel restrictions and the cancelation of large meetings," Meyers stated. "Asymptomatic dissemination certainly makes containment more difficult." Meyers pointed out that the statistics that show a distinct image over time with hundreds of new cases occurring around the world each day. Case accounts of illness are based on experiences of people from where they went and with whom they were in contact. If health officials try to separate patients rapidly, that can also distort the results.
Our results are corroborated by incidents of silent spread and that case reports in hundreds of cities across the world, "said Meyers." This shows us that outbreaks of COVID-19 may be unpredictable and involve drastic intervention.
The work was also assisted by Zhanwei Du from Texas University in Austin, Lin Wang from the Pasteur Institute in Paris, Xiaoke Xu from Dalian Minzu University, Ye Wu from Beijing Normal University and Benjamin J. Cowling from Hong Kong University. At the University of Texas in Austin, Lauren Ancel Meyers holds the Denton A. Cooley Centennial Professorship in Zoology.
The research has been funded by the United States National Health Laboratories, and China's National Natural Science Foundation.
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