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

In simplest terms, the reproductive number of a disease is a function of its transmission rate and the duration of infectious period. Transmission rate is a function of both the number of social contacts an individual has and the probability that a contact results in a transmission. Therefore, either a greater number of contacts or a higher probability per contact, such as when someone is shedding more virus or the virus is more transmissible, can increase the transmission rate. Thus, governments have opted for widespread quarantines (thereby reducing contacts) to reduce the transmission rate of COVID-19 regardless of its infectiousness. On the other hand, a long infectious period in one individual can result in a high number of resultant infections. Recovery, death, and isolation of an individual all result in a halt in that individual's ability to transmit a virus (though all such options are not equally desirable). A high transmission rate and short infectiousness period or vice versa can result in the same R0, but the implications for disease spread are different; a longer infectiousness period would result in a much later peak relative to a high transmission rate (though the number of infected people at the peak is comparable). Understanding the transmission patterns of COVID-19 can help policymakers predict critical moments in its progression, such as peak infection and the point when herd immunity has been reached and restrictions can be lifted or whether to worry about a second peak later.