Maintaining face mask use (at the amount of use 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 across nearly all scenarios explored. For example, it was always cost-effective and usually cost saving when the cost of face masks per person per day was up to $1·25. In fact, in all scenarios, it was cost-effective to maintain face mask use for about 2–10 weeks beyond the date that target vaccination coverage was achieved, with this added duration being longer when target coverage was achieved during winter versus summer. What follows are the major drivers that affected the findings.
The value of face masks increased in more than a linear manner as final vaccination coverage decreased (Figure 1, Figure 2). If the USA were to achieve an 80% vaccine coverage by March 1, 2022, simulations show that maintaining face mask use until then would avert US$14·6 billion (95% CI 13·8–15·3) in societal costs and $2·3 billion (95% CI 2·2–2·4) in third-party payer costs as well as 6·29 million (95% CI 6·28–6·3) cases, 138 600 (95% CI 137 600–139 700) hospital admissions and treatment, and 16 100 (95% CI 15 900–16 300) deaths, saving 180 000 (95% CI 172 500–187 600) QALYs (70% vaccine efficacy to prevent infection; these outcomes per 100 000 people are shown in the table; Figure 1, Figure 2). However, achieving only a 70% coverage would increase these savings to $20·6 billion (19·8–21·5) in societal costs, $3·27 billion (3·20–3·34) in third-party payer costs, 8·3 million (8·29–8·34) cases, 193 500 (192 100–194 800) hospital admissions and treatment, 22 700 (22 500–22 900) deaths, and 252 900 (243 700–262 000) QALYs.
Figure 1Simulated number of SARS-CoV-2 cases with and without face masks at different vaccination coverages
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(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 2Estimated cost savings associated with maintaining face mask use
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(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.
TableDifference between not wearing face masks and maintaining face mask use when achieving target vaccination coverages at different dates with different vaccine efficacies
Data are presented as median (IQR). The date at which vaccination coverage is achieved occurs 2 weeks after vaccination to account for the 2 weeks that it might take for the full onset of immune protection. Results are the number of cases, clinical, and economic outcomes occurring from October, 2021, to December, 2022.
If the USA were to achieve a 90% coverage by May 1, 2022, simulations show that face mask use would avert $13·3 billion (12·5–14·1) in societal costs and $2·4 billion (2·2–2·5) in third-party payer costs, as well as 6·29 million (6·27–6·30) cases, 136 700 (135 700–137 800) hospital admissions and treatment, and 16 000 (15 700–16 100) deaths, saving 181 500 (173 900–198 200) QALYs (Figure 1, Figure 2). These savings would increase to $16·7 billion (15·9–17·5) in societal costs, $2·9 billion (2·8–3·1) in third-party payer costs, 7·66 million (7·63–7·69) cases, 174 900 (173 700–176 100) hospital admissions and treatment, 20 500 (20 300–20 700) deaths, and 223 700 (215 100–232 400) QALYs if only achieving 80% coverage (Figure 1, Figure 2).
For a given final vaccination coverage level, the longer it takes to reach that level, the greater the value of face masks (Figure 1, Figure 2; table). For example, as shown, if an 80% vaccination coverage is achieved at May 1, 2022 (70% vaccine efficacy), maintaining face masks until then would avert 7·66 million cases. However, if this same coverage was reached 2 months later on July 1, then these results change to $18·7 billion (17·8–19·5) in societal costs, $3·3 billion (3·2–3·5) in third-party payer costs, 8·57 million (8·55–8·60) SARS-CoV-2 cases, 200 000 (198 000–201 000) hospital admissions and treatment, and 23 200 (23 000–23 500) deaths averted, saving 264 000 (255 000–274 000) QALYs (Figure 1, Figure 2).
Varying R0 showed that the emergence of more transmissible variants such as the delta and now omicron variants has further boosted the value of face masks (figure 1). For example, as aforementioned, when the R0 is 5, corresponding to the delta variant, maintaining face masks would avert $20·6 billion (19·8 to 21·5) in societal costs (70% coverage by March 1, 2022). A higher R0 of 10, corresponding to the omicron variant, pushes these numbers averted up to $49·5 billion (43·6 to 55·4) in societal costs, $5·2 billion (5·0 to 5·4) in third-party payer costs, and 17·9 million (17·8 to 18·1) cases versus no mask use and maintaining 1 more month (until April) provided value, averting an additional $1·5 billion (−13·7 to 6·8) in societal costs, $148·6 million (−10·4 to 307·6) in third-party payer costs, and 856 000 (710 200 to 1 000 000) cases. Lowering the R0 to 2·5, corresponding to the original virus, would lower these values to 581 350 (578 950 to 583 800) cases and face mask use would not be cost-effective.
The emergence of variants and waning immunity might also reduce vaccine effectiveness, which in turn will also increase the value of face masks (Figure 1, Figure 2; table). For example, with a 50% vaccine efficacy, maintaining face mask use until reaching a 70% coverage by March 1, 2022 would avert $82·3 billion (79·7–84·9) in societal costs and $9·1 billion (8·9–9·2) in third-party payer costs as well as 29·1 million (28·8–29·5) SARS-CoV-2 cases, 533 500 (527 700–539 300) hospital admissions and treatment, and 62 600 (61 800–63 300) deaths, saving 737 900 (714 700–762 200) QALYs. As another example, with a 30% efficacy, face mask use until reaching a 70% coverage by March 1, 2022 would avert $95·1 billion (90·2–100·0) in societal costs, $10·7 billion (10·5–10·9) in third-party payer costs, and 34·0 million (33·7–34·3) cases. Maintaining masks for 2 more months until May would be cost-effective (ICER $48 421 per QALY) averting an additional 1·2 million (0·9–1·6) cases compared to maintaining masks for 1 additional month (figure 3). Even with a 90% vaccine efficacy, face mask use provided value, averting $1·7 billion (1·4–2·1) in societal costs, $1·0 billion (0·9–1·1) in third-party payer costs, and 1·93 million (1·92–1·93) cases compared to no mask use when achieving coverage by March 1, 2022 (Figure 1, Figure 2, Figure 3).
Figure 3Simulated number of SARS-CoV-2 cases when face masks are used for different durations after the final vaccination coverage is achieved
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(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.
Increasing the effectiveness of face masks (eg, average compliance of 44·2%), decreased the total number of infections when using masks and thus increased the value of face mask wearing. For example, when an 80% vaccination coverage was achieved by March 1, 2022 (vaccine efficacy 70%; R0=5) maintaining face mask use averted $18·0 billion (17·3–18·7) in societal costs and $3·0 billion (2·9–3·1) in third-party payer costs, as well as 8·15 million (8·14–8·17) cases, 179 400 (178 400–180 400) hospital admissions and treatment, and 20 900 (20 700–21 100) deaths, saving 235 900 (228 800–242 900) QALYs.
Mask use in March, 2020, to July, 2020, with that particular combination of N95, surgical, and cloth masks, would have resulted in a cost per person per day of $0·32. Adjusting different usage and characteristics (eg, frequency of replacement and cost per mask; appendix p 8) so that the cost per person per day increased to $0·94 resulted in decreases in cost savings, but face mask use would remain cost-effective when achieving 90% coverage by July 1, 2022 (ICER $8293 per QALY) and would remain cost-effective, increasing the ICER to $36 092 per QALY, when further increasing this cost to $1·17. As another example, when increasing this cost to $1·25 per person per day, face masks would remain cost saving for most scenarios and would be cost-effective (ICER $36 092 per QALY) when achieving a 90% coverage by July 1, 2022 (70% vaccine efficacy; R0=5). When increasing the cost to $1·39 per person per day, maintaining face masks remained cost saving (appendix p 8) and would be cost-effective if achieving 80% coverage by July 1, 2022 (ICERs ≤$32 319 per QALY) and when achieving a 90% coverage by May 1, 2022 (ICERs ≤$43 161 per QALY). However, when face masks cost $1·39 per person per day, maintaining use would not be cost-effective (ICER $63 891 per QALY) if achieving 90% coverage by July 1, 2022 (appendix).
Further stratifying the population by age groups increased the number of infections and thus the impact and value of face mask wearing. For example, when achieving 70% vaccination coverage by May 1, 2022 (70% vaccine efficacy; R0=5), maintaining face mask use (18% effectiveness) until then would save $81·6 billion (78·7–84·5) in societal costs and $11·2 billion (11·1–11·3) in third-party payer costs, averting 29·8 million (29·6–30·2) cases and 668 400 (661 000–675 900) hospital admissions and treatment, saving 871 600 (838 700–904 600) QALYs.
Increasing the percentage of symptomatic individuals who remain isolated throughout their infectious period did reduce the value of face masks to some degree. However, even when assuming that 100% of people who were infectious and symptomatic stayed isolated, face mask use would still be cost saving, saving $359·7 million (−12·8 to 732·2) in societal costs and $575·9 million (503 to 648) in third-party payer costs, averting 1·62 million cases (1·56 to 1·67) and 3950 deaths (3800 to 4100; mask cost $0·32 per person per day; 50% vaccine efficacy; 70% vaccination coverage by March 1, 2022; R0=5). The only time it would not be cost-effective would be when achieving 90% coverage by Jan 1, 2022, and when vaccine efficacy is at least 70% or face mask costs more than $0·50 per person per day·
Discussion
The results of this study re-emphasise that vaccination alone is not enough to control the pandemic and prevent deaths and suffering, as well as the importance of multilayered interventions. As has been described previously, each available intervention has different limitations.
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Combining several layers of interventions can not only cover up these gaps but also further enhance each layer.
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Our study shows that face mask use can be cost-effective and, in many cases, cost saving, meaning that face mask use would pay for itself. This finding provides strong support for governments, third-party payers, and other organisations to provide face masks to the general public. Moreover, our study showed face mask use should not end as soon as certain amounts of vaccination coverage are achieved, even if these coverages exceed herd-immunity thresholds (eg, ranging from 60% for an R0 of 2·5 and 90% for an R0 of 10). That is because virus transmission does not immediately stop once such coverage levels are reached. Instead, face mask use could prevent additional COVID-19 cases until transmission eventually subsides after 2–10 weeks. Our study suggests that there are clear, finite times during which people should continue masking.
The continuing uncertainty of the pandemic further increases face masks’ value. Decreasing vaccine effectiveness, as has been the case with waning immunity and the emergence of new variants, only increases the value of face mask wearing. This is the case with increasing transmissibility of the virus, which has been seen with the omicron and delta variants and the current winter surge. Such may be the case in outbreak situations too if vaccine efficacy is lower and transmissibility is higher.
Our experiments also show the value of face mask wearing even as other interventions might change. For example, even if every person who is symptomatic from COVID-19 were to isolate themselves for the full duration of their infectious stage, face mask wearing would still be cost-effective and close to cost saving (eg, when face masks cost ≤US$0·50 and last 2 days). Such a scenario would not be very realistic given that many people do not get tested for COVID-19 or might not remain isolated throughout their infectious period.
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This finding demonstrates that although increasing testing might be helpful, it alone will not be enough to control the pandemic and will not remove the need for face mask wearing.
Additionally, our study supports face mask use across the population and not just among specific age groups or in people who have particular mixing patterns. In fact, the more we substratified the population and made mixing patterns heterogeneous, the more the value of face masks increased. This increase in value is caused by the fact that more intense mixing occurs among certain population strata, increasing transmission of the virus and the number of COVID-19 cases.
Our study also estimates the value of increasing face mask effectiveness and adherence. When increasing face mask effectiveness by 10% (implying mask compliance is 44·2%), the relative reduction in cases is greater, with a 17–20% reduction in cases, hospital admissions and treatment, and deaths. Nevertheless, even if there are shortages in more effective face masks (eg, N95 masks), wearing any face mask (eg, cloth masks) is better than not wearing one. This is because people who are infected with SARS-CoV-2 are less likely to transmit the virus to others when wearing a mask, even if it is made of cloth.
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Although our model represented the USA, our results could be applicable to other country settings. The value of face mask wearing was robust to changes in mixing patterns, vaccination coverage, vaccine efficacies, and transmission parameters, which covers a lot of the diversity seen across the world including in low-income and middle-income countries. For example, the 50% vaccine efficacy scenarios are similar to countries primarily using inactivated-virus vaccines,
54
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such as Bahrain, Chile, and Hungary
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and the 80% vaccination coverage with 70% vaccine efficacy scenario is similar to current situations in Spain and Australia.
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These results can help provide a general estimate for how long after reaching different coverage levels masks can still provide value.
All models, by definition, are simplifications of real life and cannot account for every possible outcome.
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Model inputs drew from various sources and time points during the pandemic, and new data on SARS-CoV-2 continues to emerge. We did not vary the effectiveness of face masks on the transmissibility of the virus over the duration of the simulation, however this effectiveness might vary from day to day and over time and with state-level and local-level policies.
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Our scenarios assume coverage of the entire population; however, some populations are not yet eligible for vaccination (eg, children aged
This study helps quantify the value of maintaining face mask use until certain vaccination coverages are achieved and how doing so can be not just cost-effective, but even cost saving under a wide variety of circumstances. We found substantial value in continuing face mask wearing 2–10 weeks beyond the achievement of target vaccination coverage thresholds to reduce residual SAR-CoV-2 transmission. 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.
All authors conceived and designed the question, model, and experiments. All authors collected, accessed, and verified the data. SMB, KJO, KLC, PTW, MCF, SSS, and SNC developed the model. SMB, KJO, MCF, MEB, US, KLC, SNC, PTW, PJH, and BYL parameterised the model. All authors analysed the data. SMB, KJO, MCF, MEB, US, KLC, PTW, SNC, PJH, and BYL helped draft the paper. All authors edited the paper and were included in the decision to submit for publication.
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