Explaining the Bomb-Like Dynamics of COVID-19 with Modeling and the Implications for Policy

Gary Lin; Alexandra T Strauss; Maxwell Pinz; Diego A Martinez; Katie K Tseng; Emily Schueller; Oliver Gatalo; Yupeng Yang; Simon A Levin; Eili Y Klein

Finally, the troubling implication of these results is that asymptomatic rates are estimated to be ~50%. Based on the fits from the model, this would suggest that the R0 of COVID-19 may be higher than 2.5. A high R0 combined with large numbers of asymptomatic and mildly infected individuals could account for the "bomb-like" dynamics of COVID-19. In New York City, the rate of confirmed cases has been doubling roughly every 2 days. This is faster even than Italy where the rate of doubling was approximately every three days. Recent data on mortality in the NYC region suggests that this rapid increase in cases is not just the effect of rapid increased testing, as the number of deaths is growing at a similar rate as the case load with an approximate two-week lag ( Figure 5 ). This mortality rate is, at least for the moment, substantially higher than the rate in Italy (Figure 6 ). This suggests that densely populated urban areas may facilitate more rapid spread of the disease and have even higher reproductive numbers. Given the strong connectivity between China and NYC, it is likely the first cases of COVID-19 arrived in NYC by late January, yet the first case was not observed until late February and there was no "explosion" until mid-March. This should be a cautionary tale to other cities that are not as connected to international travel as NYC or are in the Southern Hemisphere, where potential seasonal differences may have led to lower transmission rates in February and March [31] . Postponing policy action until the outbreak is well underway, as NYC and Italy did, is thus much less effective in containing the virus. Only by extensive and early restrictions can the bomb-like dynamics of the disease be averted. In South Korea, the dynamics initially appear similar, but the introduction of widespread testing likely led to the discovery of much larger numbers of less severe cases, which bent the curve. However, as the case of Hong Kong demonstrates, relaxing these policies before the disease has spread widely enough to provide herd immunity leads to rapid growth in cases within a couple of weeks [32] . Without a vaccine, cities and countries will need to manage the spread of the virus so that the number of hospitalized individuals will not exceed capacity. This is a difficult option but the only rational policy until more progress is made in vaccine development or therapeutics.