Maintaining face mask use before and after achieving different COVID-19 vaccination coverage levels: a modelling study

Abstract

Background: Face mask wearing has been an important part of the response to the COVID-19 pandemic. As vaccination coverage progresses in countries, relaxation of such practices is increasing. Subsequent COVID-19 surges have raised the questions of whether face masks should be encouraged or required and for how long. Here, we aim to assess the value of maintaining face masks use indoors according to different COVID-19 vaccination coverage levels in the USA.

Methods: In this computational simulation-model study, we developed and used a Monte Carlo simulation model representing the US population and SARS-CoV-2 spread. Simulation experiments compared what would happen if face masks were used versus not used until given final vaccination coverages were achieved. Different scenarios varied the target vaccination coverage (70-90%), the date these coverages were achieved (Jan 1, 2022, to July 1, 2022), and the date the population discontinued wearing face masks.

Findings: Simulation experiments revealed that maintaining face mask use (at the coverage seen in the USA from March, 2020, to July, 2020) until target vaccination coverages were achieved was cost-effective and in many cases cost saving from both the societal and third-party payer perspectives across nearly all scenarios explored. Face mask use was estimated to be cost-effective and usually cost saving when the cost of face masks per person per day was ≤US$1·25. In all scenarios, it was estimated to be cost-effective to maintain face mask use for about 2-10 weeks beyond the date that target vaccination coverage (70-90%) was achieved, with this added duration being longer when the target coverage was achieved during winter versus summer. Factors that might increase the transmissibility of the virus (eg, emergence of the delta [B.1.617.2] and omicron [B.1.1.529] variants), or decrease vaccine effectiveness (eg, waning immunity or escape variants), or increase social interactions among certain segments of the population, only increased the cost savings or cost-effectiveness provided by maintaining face mask use.

Interpretation: Our study provides strong support for maintaining face mask use until and a short time after achieving various final vaccination coverage levels, given that maintaining face mask use can be not just cost-effective, but even cost saving. The emergence of the omicron variant and the prospect of future variants that might be more transmissible and reduce vaccine effectiveness only increases the value of face masks.

Funding: The Agency for Healthcare Research and Quality, the National Institute of General Medical Sciences, the National Science Foundation, the National Center for Advancing Translational Sciences, and the City University of New York.

Figure 1

Simulated number of SARS-CoV-2 cases with and without face masks at different vaccination coverages (A) Vaccination with 70% efficacy against infections, with SARS-CoV-2 R₀=5. (B) Vaccination with 70% efficacy against infections, with SARS-CoV-2 R₀=8. (C) Vaccination with 50% efficacy against infections, with SARS-CoV-2 R₀=5. Vaccination coverage is defined as the time at which immune protection was achieved, 2 weeks after vaccination.

Figure 2

Estimated cost savings associated with maintaining face mask use (A) Direct medical cost savings when maintaining face mask use. (B) Productivity cost savings when maintaining face mask use. (C) Total societal cost savings when maintaining face mask use. Final coverage defined as when immune protection is achieved, 2 weeks after vaccination.

Figure 3

Simulated number of SARS-CoV-2 cases when face masks are used for different durations after the final vaccination coverage is achieved (A) 70% vaccine efficacy with SARS-CoV-2 R₀=5, and vaccination coverage achieved by Jan 1, 2022. (B) 70% vaccine efficacy with SARS-CoV-2 R₀=8, and vaccination coverage achieved by Jan 1, 2022. (C) 70% vaccine efficacy with SARS-CoV-2 R₀=5, and vaccination coverage achieved by March 1, 2022. (D) 70% vaccine efficacy with SARS-CoV-2 R₀=8, and vaccination coverage achieved by March 1, 2022. (E) 50% vaccine efficacy with SARS-CoV-2 R₀=5, and vaccination coverage achieved by Jan 1, 2022. (F) 50% vaccine efficacy with SARS-CoV-2 R₀=5, and vaccination coverage achieved by March 1, 2022. Maintaining face mask use for longer provided more benefits with lower vaccine efficacies and with increases in R₀. Note the differences in scales across the panels, which was done to more readily see when outcomes levelled off with increases in the time face masks were used.