Researchers from the University of Hong Kong (HKU) have discovered that China's nonpharmaceutical interventions drastically reduced the serial interval of COVID-19, according to the paper published on the world's leading academic journal Science on July 21.

Serial interval, a key metric of epidemics, refers to the duration between the symptom onset of two consecutive cases in the chain of transmission. For example, if A infects B, the serial interval is the time between the first symptoms of A and B.

The researchers compiled a database of 1,407 COVID-19 transmission pairs, and focused on 677 pairs whose symptom onset dates and social relationships were available for both the infectors and infectees. The infectors among the 677 pairs developed symptoms from January 9 through February 13, 2020.

They modeled the spread of COVID-19 in China, and found that "mean serial intervals of COVID-19 have shortened substantially from 7.8 days to 2.6 days within a month (January 9 to February 13, 2020)," according to the research paper.

"This change is driven by enhanced non-pharmaceutical interventions, in particular case isolation," it wrote.

The researchers said that early isolation translates into shorter serial intervals days, and delayed isolation is associated with a longer serial interval days.

Improvements in identification and isolation of cases shortened the serial intervals, which reduced the chance of transmission later in illness.

Nature, another top academic journal said the finding "underscores the success of China's testing and isolation efforts."

The research will further improve the assessment of the novel coronavirus transmission dynamics, the prediction of future incidence, and the estimation of the efficacy of containment measures, said the HKU on its website.