Worldwide Effectiveness of Various Non-Pharmaceutical Intervention Control Strategies on the Global COVID-19 Pandemic: A Linearised Control Model

Naude, J.; Mellado, B.; Choma, J.; Correa, F.; Dahbi, S.; Dwolatzky, B.; Dwolatzky, L.; Hayasi, K.; Lieberman, B.; Maslo, C.; Monnakgotla, K.; Ruan, X.; Stevenson, F.

Background COVID-19 is a virus which has lead to a global pandemic. Worldwide, more than 100 countries have imposed severe restrictions regarding freedom of movement amongst their citizens in a bid to slow the spread of the virus. These restrictions, which are part of a set of non-pharmaceutical interventions, have recently been classified by the Oxford COVID-19 Government Response Tracker (OxCGRT) team and a nominal index measure has been defined for use by the wider international community. We address the use of this index measure to establish the degree and characteristics of control of the transmission rate of the virus within a representative sample of countries in the World and states in the United States of America. Methods Country specific, Susceptible-Infected-Recovered-Deaths (SIRD) models with latent dynamics were constructed using publicly available data for 23 countries and 25 states of the United States of America. Each of the models were linearised and classical frequentist error propagation was applied to them individually. The time varying, observable model parameters were extracted for each day that data was made available. The OxCGRT stringency index, p, was used to regress against these model parameters. The regression of the transmission rate as a function of p in each locale was through a linear parameter _s. In addition, macroscopic indices from the World Bank were used to explore inter-country variation in the measured parameters. Results The world average was _s=0.01 (95% CI 0.0102 - 0.0112) with an ensemble standard deviation of 0.0017 (95% C.I. 0.0014 - 0.0021), strongly indicating a universal behavior. While lockdown measures have been successful in curbing the spread, our study indicates that removing them too swiftly will result in the resurgence of the spread within one to two months. Reducing the stringency index by 10 will delay reaching the apex by about 6 months, where reducing it by 20 will delay by only four months. During the post-lockdown period it is essential to increase _s. For the system to remain sub-critical, the rate with which _s increases should outpace that of the decrease of the stringency index. The spread of the virus is found to be insensitive to the Gini index and other socio-economic indexes. The typical adjustment time to see the effects of control varied between 1.49 days for Peru and 38.09 days for Sweden. In the United States, the typical adjustment time to see the effects of control varied between 1.41 days for Colorado to 15.91 days for Ohio. Interpretation Given the measured characterisations of each locale, the effects of any change in non-pharmaceutical intervention may be anticipated and predictions can be made regarding the possible case load which is specific to that environment. This is accomplished by specifying an acceptable level of transmission, {beta}_f, given the prevailing economic and social constraints which uniquely determines an overall stringency of intervention level p. As a policy maker, there are possible intervention combinations to choose from and a combination must be selected that achieves p or greater.