In China, a key metric of epidemics called the serial interval shrank drastically soon after the new coronavirus’s arrival — a finding that underscores the success of China’s testing and isolation efforts. The serial interval is the average time between the onset of symptoms in a chain of people infected by a pathogen. Benjamin Cowling at the University of Hong Kong and his colleagues modelled the spread of SARS-CoV-2 in China and found that the serial interval plummeted from 7.8 days to 2.6 days over a 5-week period starting on 9 January (S. T. Ali et al. Science http://doi.org/gg5mpc; 2020).
The researchers say that early isolation of cases prevented transmission that would otherwise have occurred later in an infectious period, leading to fewer cases and slowing the spread of the virus. As a result, most of the remaining transmissions occurred either before infected people showed symptoms or early in the symptomatic phase, and the serial interval shrank. The authors suggest the serial interval distribution be used in real time to track the changing transmissibility of the virus.
Original study published in Science (July 21, 2020):