Prof. Dr. Ahmet Rasim Küçükusta

The simplest interpretation of our results is that 1) aerosol transmission of Ab can occur and that 2) the propensity for this transfer is, unsurprisingly, directly related to the amount of nasal/oral Ab found within those in the population possessing immunity. We have yet to encounter an equally parsimonious interpretation, although admittedly this does not mean one does not exist. The concept of herd immunity is a central tenant of public health vaccination campaigns. Overt blockade of infection as well as a reduction in viral transmission downstream of a breakthrough infection are widely accepted conceptual mechanisms by which vaccination-induced immunity in specific individuals protects nonimmune community members. With this in mind, it stands to reason that aerosol transmission of Abs could also contribute to host protection and represent an entirely unrecognized mechanism by which passive immune protection may be communicated.

As cross-reactivity between seasonal coronavirus spike proteins and the RBD of SARS-CoV-2 has not been observed, we do not believe that our results have been unduly influenced by subjects’ prior exposure to seasonal coronavirus. Although there is some small degree of cross-reactivity between the S2 domains of SARS-CoV-2 and the OC43 seasonal strain (5, 6), this does not extend to the S1 domain or the more limited RBD. Were this to be true, it is arguable that the course of the pandemic would have been substantially altered for the better.

Unfortunately, the difficulty in recruiting participants from unvaccinated households in conjunction with the availability of the vaccines for children under the age of 5 y rendered continued sample acquisition unsustainable. As such, we were unable to determine whether the aerosol transfer of IgA might achieve statistical significance from increased sample evaluation, nor were we able to devise any assay suitable for determining the biological relevance of the observed aerosol transfer of IgG. However, whether Ab transfer mediates host protection will be a function of exposure, and it seems reasonable to suggest, all things being equal, that any amount of Ab transfer would prove useful to the recipient host. With the documented benefits of parental vaccination in reducing the risk of infection in the unvaccinated children in the same home (7), it is tempting to speculate that aerosol-mediated Ab transfer may have possibly contributed to the reported findings. It seems likely that nasal swabs originally collected for monitoring SARS-CoV-2 transmission in this study could be repurposed for examining SARS-CoV-2–specific IgG and IgA within the vaccinated adults as well as noninfected family members, potentially providing the statistical power necessary for validating the conclusions drawn in the current study.