How much leeway is there to relax COVID-19 control measures?

Area of Science:

• Epidemiology
• Mathematical Modeling
• Public Health Policy

Background:

• Non-pharmaceutical interventions (NPIs) successfully controlled COVID-19, leading to economic and border reopenings.
• Low population immunity post-NPIs created substantial risk for COVID-19 resurgence upon increased social contact.

Purpose of the Study:

• To develop a Bayesian method for estimating COVID-19 reopening "leeway" or the required intervention strength for control.
• To assess reopening risks and the impact of imported cases across diverse jurisdictions.

Main Methods:

• A Bayesian approach was used to model COVID-19 epidemics and estimate leeway.
• Timing and strength of initial NPIs were analyzed, comparing early vs. later reopening estimates.
• Risks of reopening and projected case burden from imported infections were quantified.

Main Results:

• Jurisdictions exhibited widely varying leeway to reopen; some had substantial capacity (Japan, Germany), others little (UK, Washington), and some none (Sweden, California).
• Increases in contact rates of 1.5-2 fold posed a high probability (>0.7) of exceeding previous COVID-19 peak sizes in many regions.
• Even minimal case importation (1 case/week) could lead to ~100 additional cases over six weeks in some scenarios.

Conclusions:

• Estimates of reopening leeway provide a quantitative basis for public health decisions.
• A cautious approach to reopening economies and borders, with robust transmission monitoring, is recommended to manage COVID-19 risks.