RR:C19 Evidence Scale rating by reviewer:
Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.
In this paper the authors model the impact of TTI and mask wearing on SARS-CoV-2 transmission and conclude that though there could be an impact of face masks use in community and secondary school settings, that further interventions such as TTI will be needed.
The paper uses an individual based model to model transmission in the UK. This model has been used for modelling SARS-CoV-2 transmission in other countries. A strength of the model is the ability to model TTI. The model models transmission in different settings (school, workplace etc.), though it would have been helpful to have more description of how movement between these places and contacts in each setting were parameterised for the UK.
The paper brings to attention important things about mask wearing such as that masks will not be worn in homes, and therefore will not impact transmission at home and discusses the use of masks in different places within a school. Though the latter is not modelled explicitly as far as I can tell.
However, I have some reservations about the parameterisation of the efficacy and coverage of masks. As this is a fundamental part of the conclusions, it would warrant much greater description and discussion.
For the efficacy, it would be good to have great description of how the numbers in the meta-analysis cited and relate to the way mask use is parameterised in the model, and how the settings of the studies in the meta-analysis relate to the settings in which the mask use is being modelled.
Similarly, it would be helpful to have further description of how the coverage is modelled within the model. Does this assume that if a person wears a mask, they wear it for all contacts? How does this interact with the efficacy? The latter columns of Table 2 are hard to interpret and to understand how these numbers have been arrived at.
I have some doubts about the long timeframe of the model. The authors note that this is fraught with uncertainty. I do understand the rationale for understanding whether such interventions delay the peak, but I think that given the uncertainty it would be better to focus on the immediate modelled impact, rather than over a year down the line.
The study of masks has been difficult as the authors note. This becomes even more complex when projecting the impact of masks within mathematical models where it is necessary to quantify the impact. I think this study is potentially informative, with the weaknesses listed above about how masks are parameterised in the model.