Social restriction versus herd immunity policies in the early phase of the SARS-CoV-2 pandemic: A mathematical modelling study
Wiwat Chancharoenthana,1 Asada Leelahavanichkul,2,3 Sutatip Chinpraditsuk,4 Krit Pongpirul,5,6 Supitcha Kamolratanakul,1 Weerapong Phumratanaprapin,1 Polrat Wilairatana,1 Punnee Pitisuttithum1
Affiliations:
1 Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
2 Department of Microbiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
3 Translational Research in Inflammation and Immunology Research Unit (TRIRU), Department of Microbiology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
4 Hospital for Tropical Diseases, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
5 Thailand Research Center for Health Services System (TRC-HS), Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
6 Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
Abstract
Background: Two main strategies to cope with the coronavirus disease 2019 (COVID-19) pandemic—lockdown (social restriction) and non-lockdown (herd immunity plan)—have been implemented in several countries.
Objective: This study aims to statistically compare the outcomes of the two strategies, represented by data from Thailand and Sweden, respectively.
Methods: Data for COVID-19 pandemic control from Thailand, representing social restriction, versus data from Sweden, representing the herd immunity plan, collected from January 13 to May 31, 2020, were analyzed by using the SIR (susceptible, infectious, recovered) model.
Results: The SIR model analysis demonstrated a beneficial effect of each model on the attenuation of the mortality rate, with lower mortality in social restriction and shorter overall pandemic duration in the herd immunity plan. However, the herd immunity plan demonstrated a higher mortality rate than social restriction (46.9% versus 1.9%) despite the later entry of the virus in Sweden. When the SIR model was used for predicting the COVID-19 status, Sweden was shown to likely end its COVID-19 epidemic earlier than Thailand (268 vs. 368 days). With the nonlinear estimation, at least one log difference between total confirmed cases versus active cases could be used as an indicator for relaxation of the lockdown policy in Thailand.
Conclusions: Both the social restriction and herd immunity plans are beneficial for COVID-19 pandemic control in terms of the amelioration of pandemic mortality. The cumulative number of total recovered cases might be a potential parameter that could be used for determining the policy direction for COVID-19 control.
Key words: COVID-19, control strategy, lockdown, mortality rate, SARS-CoV-2,