Researchers from the Los Alamos National Laboratory (LANL) concluded in a recent study that the CCP virus could have been more contagious when it first spread in China than the World Health Organization (WHO) reported.
The research, published in the scientific journal Emerging Infectious Disease on April 7, found that the virus’s reproduction number, or R0 (pronounced “R naught”), in Wuhan—where the outbreak first erupted—was initially 5.7.
In other words, each infected individual passed the virus on to 5.7 people on average.
Most of the 140 people tested positive for the virus between Jan. 20 and Jan. 26 with epidemiological links or exposure to Wuhan, the study stated, citing information released by Chinese health authorities. Most of them tested positive outside of Hubei Province, where Wuhan is the capital city.
The researchers explained their rationale for analyzing cases outside of Hubei Province.
“By the time cases were confirmed in provinces outside Hubei, all of the provinces of China had access to diagnostic kits and were engaging in active surveillance of travelers out of Wuhan,” the researchers stated.
At the time, “the healthcare systems outside Hubei were not yet overwhelmed with cases and were actively searching for the first positive case, leading to much lower bias in the reporting in each province compared with the time series of confirmed cases in Wuhan,” they stated.
It should be noted that R0 isn’t a fixed number; it can change over time depending on a number of factors, such as climate or quarantining policies enacted by local authorities. How quickly the virus spreads can vary by country and region.
The WHO has at least on two occasions given an estimate of the virus’s reproduction number. On Jan. 23, it wrote that the human-to-human transmission rate (R0) in China was estimated to be between 1.4 and 2.5.
In its latest “research roadmap” report published in March, the WHO said the R0 is estimated to be 2.2, citing a January study by a group of researchers from Hong Kong and China, including George F. Gao, director of China’s Center for Disease Control and Prevention. That study was based on data from 425 cases in Wuhan.
An R0 of less than 1 means that a viral transmission is likely to die out. An R0 higher than 1 means it will grow, perhaps exponentially.
Knowing the R0 is important for health officials, since it is a “useful tool for understanding the most effective practices to slow the virus’s spread,” wrote Antonio Regalado, senior editor for MIT Technology Review, in a March article.
Regalado stated: “It’s a way to calculate, for example, how extensive and extreme social distancing must be. If you can cut the transmission rate by more than half, you have effectively stopped the spread.”
LANL researchers also used mobile phone data in China, which tracked the number of daily travelers in and out of Wuhan, to deduce that the number of infections during the early outbreak in Wuhan doubled in just 2.3 to 3.3 days, contrasting the more than six days suggested by other studies.
“This finding would have important implications for forecasting epidemic trajectories and the effect on healthcare systems as well as for evaluating the effectiveness of intervention strategies,” LANL researchers said.
For example, researchers said that quarantining individuals and contact-tracing people who show symptoms of the virus is likely ineffective, since a significant portion of the virus transmission was predominantly driven by asymptomatic carriers.
“When 20% of transmission is driven by unidentified infected persons, high levels of social distancing efforts will be needed to contain the virus,” the study stated.