Note: for the following comments, #1 is supportive and does not need a reply. Items #2-#4 express relatively minor concerns. The most important issues are raised in comments #5-#9.

1. I support the use of the editorial pages of Indoor Air to express well-informed opinions pertinent to the scope of this journal, i.e. the nexus of (nonoccupational) built environments and human health.
2. Clearly the topic of building features that affect the spread and consequences of the COVID-19 pandemic is relevant. Indoor transmission of infectious diseases has been explored in the journal prior to the current pandemic. Furthermore, during the past two years, among the 12 issues published, most editorials (8 of 13) have been concerned with some aspect of indoor airborne infectious disease transmission. A weakness of the present submission is that its framing is largely independent of this substantial and relevant history. The editorial would be stronger if its contributions were stated in the context of what is new and different compared with what has already been presented in the pages of this journal.
3. Another weakness (error) in the framing is the use of the shorthand phrase “respiratory disease” to refer to “infectious respiratory diseases” or “communicable respiratory diseases.” Of course, there are many respiratory diseases that can occur independent of viral or bacterial agents, such as bronchitis, emphysema, asthma, and lung cancer.
4. I was surprised to see the statement that “measles … was classified as a droplet disease until the 1980s.” That statement seems contradicted by the publication of a widely cited article by EC Riley et al., “Airborne spread of measles in a suburban elementary school,” American Journal of Epidemiology 107, 421, 1978. That article uses a modeling approach similar to the one utilized in Peng et al. (reference 6), which is the basis of the figure.
5. The quantitative information used to prepare Figure 1 (left) should be completely specified. In particular, the quanta emission rates used to plot the six lines (3 diseases x 2 emission levels) should be stated.
6. In Figure 1 (left), a comparison is made between “close proximity” conditions and “shared room air” conditions. As indicated in the caption, the risk of transmission is only considered for a 10-minute exposure period. For certain types of interactions and occupancy, that might be appropriate, but these would represent a very narrow slice of all indoor occupancy circumstances: a physician visit, or a conversation at a party, perhaps; but not a shared meal, nor a full 8-hour work shift. The selection of a 10-minute exposure duration likely biases the sample in such a way to exaggerate the risk of close proximity compared with shared room air.
7. In Figure 1 (right), it seems that some important information is not stated. I cannot see how absolute values (%) of the attack rate can be expressed in relation to a “relative” risk parameter. What is the assumed quanta emission rate in this case? A similar concern arises about this claim: “These results enable the possibility of rapidly estimating the absolute and relative risk of infection….”
8. The presented equation for the “relative risk parameter” (Hr) is puzzling. How can the risk of transmission be independent of occupant density? In the Japanese (and now WHO) guidance for COVID-19, one should avoid the “Three C’s” — Closed spaces, Crowded places, and Close-contact settings. The ventilation term that appears in the denominator pertains to the degree to which a space is “Closed.” The “Close-contact” avoidance is built into the close proximity aspect, which the equation does not address. But surely the risk of disease transmission would vary with the density of occupation (“Crowded places”). That aspect, which is practical to control, ought to feature into an effort to “make spaces safer from shared-room airborne transmission.”
9. Figure 1(right) indicates some success in modeling COVID-19 superspreading events. It is a large extrapolation to assume that this model would then apply to describe most of the disease transmission processes. There are many potential pathways for transmission of the viral agent from infectious to susceptible. The poor state of knowledge about airborne transmission in the infection prevention and control (IPC) community suggests that one may justifiably doubt the completeness of the classic three-path classification system (droplet, fomite, aerosol). I would caution against overconfidence in generalizing from what can be modeled to the vastly more numerous circumstances in which the transmission pathway isn’t known and can’t be reliably inferred.

Please see attached remarks.