Can Koreans be ‘FREE’ from mask wearing?: Advanced mathematical model can suggest the idea

Background It was found that more than half of the population in Korea had a prior COVID-19 infection. In 2022, most nonpharmaceutical interventions, except mask-wearing indoors, had been lifted. Discussions about easing the indoor mask mandate are ongoing. Methods We developed an age-structured compartmental model that distinguishes vaccination history, prior infection, and medical staff from the rest of the population. Contact patterns among hosts were separated based on age and location. We simulated scenarios with the lifting of the mask mandate all at once or sequentially according to the locations. Furthermore, we investigated the impact of a new variant assuming that it has higher transmissibility and risk of breakthrough infection. Findings We found that the peak size of administered severe patients might not exceed 1,100 when the mask mandate is lifted everywhere, and 800 if the mask mandate only remains in the hospital. If the mask mandate is lifted in a sequence (except hospital), then the peak size of administered severe patients did not exceed 650. Moreover, if the new variant have both of higher transmissibility and immune reduction therefore the effective reproductive number of the new variant is approximately 3 times higher than the current variant, additional interventions may be needed to keep the administered severe patients from exceeding 2,000, which is the critical level we set. Interpretation Our findings showed that the lifting of the mask mandate, except in hospitals, would be applicable more manageable if it is implemented sequentially. Considering a new variant, we found that depending on the population immunity and transmissibility of the variant, wearing masks and other interventions may be necessary for controlling the disease. Funding This paper is supported by the Korea National Research Foundation (NRF) grant funded by the Korean government (MEST) (NRF-2021M3E5E308120711). This paper is also supported by the Korea National Research Foundation (NRF) grant funded by the Korean government (MEST) (NRF-2021R1A2C100448711). This research was also supported by a fund (2022-03-008) by Research of Korea Disease Control and Prevention Agency. Evidence before this study There are numerous studies in modelling transmission dynamics of COVID-19 variants but only a few published works tackle the lifting of mask mandate considering the omicron variant, although these studies did not consider unreported cases, variants, and waning immunity. Furthermore, there is no age-structured modeling study which investigated the effect of lifting mask mandate considering high immune state of the population, contributed by both of natural infection and vaccination. Added value of this study Our mathematical model considered key factors such as vaccine status, age structure, medical staff, prior infection, and unreported cases to study the COVID-19 epidemic in Korea. Updated data and variant-specific parameters were used in the model. Contact patterns in the household, school, work, hospital and other places are considered separately to make the model applicable to the mask mandate issue. Seasonality and scenarios on possible future variants are also included in this study. Implications of all the available evidence With mask wearing as one of the remaining non-pharmaceutical interventions in Korea and other countries, this study proposes strategies for lifting the mask mandates while ensuring that cases remain manageable. A variant-dependent factor is incorporated into the model so that policymakers could prepare proactive intervention policies against future variants. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This paper is supported by the Korea National Research Foundation (NRF) grant funded by the Korean government (MEST) (NRF-2021M3E5E308120711). This paper is also supported by the Korea National Research Foundation (NRF) grant funded by the Korean government (MEST) (NRF-2021R1A2C100448711). This research was also supported by a fund (2022-03-008) by Research of Korea Disease Control and Prevention Agency. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced are available online