Multi-chain Fudan-CCDC model for COVID-19 -- a revisit to Singapore's case

Hanshuang Pan; Nian Shao; Yue Yan; Xinyue Luo; Shufen Wang; Ling Ye; Jin Cheng; Wenbin Chen

The idea of multi-chain was first introduced by Nian Shao and Wenbin Chen on Feb They found that there was a sudden turn in growth rate, just as described in Figure 1, shown in a semi-log way. Our group suspected that a stronger transmission chain had occurred, so we began to develop a multi-chain Fudan-CCDC model. Based on the new model and the public data, we identified the start date of the new transmission chain in South Korea was around Feb 10, and thus held the view that there was a new source emerging at that time. Then we announced our finding [2] on Feb 20. Later, it was confirmed by the news [1] that there was indeed a case of super spreader on Feb 7. Singapore had been successful in disease prevention and control. Since then, one member of our group, Hanshuang Pan, has been continually tracking the data. Unexpectedly, in late February, a sudden rise occurred, see Figure 2 We show in Figure 2 the curve fitting for Singapore's data by the Fudan-CCDC model, on Feb 17 and Mar 1, respectively. We see in Figure 2 (a) that on Feb 17, the Fudan-CCDC model had predicted that the increment of confirmed cases would be zero on Feb 27, and remained stable for the next ten days. However, on the crucial day Feb 27, an unexpected rise occurred in Singapore's data (see Figure 2 (b)), which caused our vigilance. Till Mar 1, this new upward trend was so obvious that it could not be explained by the single chain Fudan-CCDC model any longer. Therefore, we began to consider the application of the multi-chain Fudan-CCDC model, and revisit Singapore's case.