Medical Brief 298 - 16 April 2020
"New modelling research suggests that China’s aggressive control measures appear to have halted the first wave of COVID-19 in areas outside Hubei province, the epicentre of the epidemic. However, given the substantial risk of the virus being reintroduced from abroad, and with economic activity increasing, real-time monitoring of COVID-19 transmissibility and severity is needed to protect against a possible second wave of infection, researchers say.
The study estimates that in regions outside Hubei, the instantaneous reproductive number of COVID-19 – the average number of cases generated by a single infected individual during the outbreak – fell substantially after lock down measures were introduced on 23 January, 2020, and has remained below 1 since then – suggesting that the epidemic has shifted from one that is expanding rapidly to one that is slowly shrinking. (The higher the reproductive number, the more transmissible the virus is and the higher the risk for rapid spread. When the reproductive number falls below one, the epidemic is likely to die out.)
However, mathematical modelling to simulate the impact of relaxing current control measures, suggests that premature lifting of these interventions will likely lead to transmissibility exceeding 1 again, resulting in a second wave of infection.
The findings are critical to countries globally that are in the early phases of lock down because they warn against premature relaxation of strict control measures, researchers say. However, the study did not specifically examine the effect of each intervention, or which one was most effective in containing the spread of the virus.
“While these control measures appear to have reduced the number of infections to very low levels, without herd immunity against COVID-19, cases could easily resurge as businesses, factory operations, and schools gradually resume and increase social mixing, particularly given the increasing risk of imported cases from overseas as COVID-19 continues to spread globally,” says Professor Joseph T Wu from the University of Hong Kong who co-led the research."
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