The authors describe several monoplex assays for human herpesviruses 1-5 with the potential application, in a multiplex format, to population-based cohort studies. They assert that established, gold-standard reference assays have been used to validate the sensitivity and specificity of their assays. Further clarification of the approach used, and several statements contained within this publication are needed. Firstly, in the reference panels and reference assays section, it is stated that varicella-zoster virus (VZV) sera were obtained from shingles/zoster studies and later it is added that sera from VZV positive blood donors were tested as well. The source of the 83 VZV IgG negative sera is unclear. Patients with shingles present with very high levels of VZV IgG which are of high avidity (1), so depending upon how many sera from such patients were tested the population data in this paper may be unrepresentative of most populations. In varicella vaccinated populations, VZV IgG levels may be much lower and avidity reduced (2). The VZV time-resolved fluorescence immunoassay (VZV TRFIA) referred to in the paper was developed by me and the reference to McDonald et al (2) in the Discussion as having developed it is inappropriate in this context and the following suggested references (3-5) are more relevant. VZV TRFIA has been compared with the gold-standard FAMA assay in varicella vaccinated individuals and the sensitivity and specificity varied with dose and the time of sampling (6). The suggestion by Brenner et al. that their assay showed substantial agreement with FAMA on the basis of high concordance with VZV TRFIA is highly questionable because published, relevant VZV TRFIA versus FAMA data in non-vaccinated populations is very limited. It would be helpful to see scatterplots of VZV TRFIA versus the various antigens tested by Brenner et al.
For all markers, it would have been useful to see data informing the limits of detection and reproducibility of the monoplex assays and multiplex assay. It would be interesting to learn the views of HSV experts regarding the adoption of LIAISON HSV-2 IgG as a reference assay and the absence of an HSV-1 reference assay and panel. Finally, a key consideration is the portability of the multiplex technology or is it proposed that all studies be undertaken by the same laboratory? I strongly advise external validation of these monoplex/multiplex assays and a key question would be how easily could they be established in external laboratories? I failed to see the use of quality control sera or standard sera; therefore, variabilities in assay data may represent altered assay performance or genuine differences in the population antibody levels measured. Some of these issues were addressed by the European Seroepidemiology Network (7, 8) and the approaches adopted facilitated international comparisons of seroprevalence.

References
1. Warren-Gash C, Forbes H, Maple P, Quinlivan M, Breuer J. Viral load and antibody boosting following herpes zoster diagnosis. Journal of Clinical Virology 2018; 103: 12-15. https://doi.org/10.1016/j....
2. McDonald SLR, Maple PAC, Andrews N, Brown KE, Ayres KL, Scott FT, Al Bassam M, Gershon AA, Steinberg SP, Breuer J. Evaluation of the time resolved fluorescence immunoassay (TRFIA) for the detection of varicella zoster virus (VZV) antibodies following vaccination of healthcare workers. Journal of Virological Methods 2011; 172: 60-65. https://doi.org/10.1016/j...
3. Maple PAC, Gray J, Breuer J, Kafatos G, Parker P, Brown D. Performance of a time resolved fluorescence immunoassay for measuring Varicella Zoster virus immunoglobulin G levels in adults and comparison with commercial enzyme immunoassays and Merck glycoprotein enzyme immunoassay. Clinical and Vaccine Immunology 2006; 13: 214-218. https://doi.org/10.1128/C...
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