Virucidal Activity of World Health Organization–Recommended Formulations Against Enveloped Viruses, Including Zika, Ebola, and Emerging Coronaviruses

Siddharta, Anindya; Pfaender, Stephanie; Vielle, Nathalie Jane; Dijkman, Ronald; Friesland, Martina; Becker, Britta; Yang, Jaewon; Engelmann, Michael; Todt, Daniel; Windisch, Marc P.; Brill, Florian H.; Steinmann, Joerg; Steinmann, Jochen; Becker, Stephan; Alves, Marco P.; Pietschmann, Thomas; Eickmann, Markus; Thiel, Volker; Steinmann, Eike

eviation: nd, not detected. usability of these formulations in viral outbreak situations. In the case of ZIKV, specific viral inactivation data are lacking, and consequently disinfection guidelines are based on data obtained from other members of the flaviviruses. So far, 1 recent study by Müller et al reported that ZIKV was inactivated by classical inactivation methods including ultraviolet light [11] . Zika virus was readily reduced in viral titers by the WHO formulations, similar to the other member of the family of Flaviviridae, HCV. These findings are supported by earlier analyses of the environmental stability and inactivation profiles of HCV, which showed strong virucidal effects of the main WHO formulation ingredients ethanol and isopropanol [12] . For EBOV, limited data on the efficacy of virucidal products are available because these viruses require high biosafety level laboratories. The Centers for Disease Control and Prevention advises "suitable disinfectant solutions include 0.5% sodium hypochloride as well as 2% glutaraldehyde and phenolic disinfectants (0.5-3%)" for EBOV inactivation [13] . The comparative inactivation analyses of all viruses tested revealed that the CoVs, in particular SARS-CoV, were the most susceptible viruses to WHO formulation treatment. The degree of susceptibility of the different viruses to the WHO formulation likely depends on the specific surface properties of the lipophilic envelope of the respective virus. We could show by a comparative inactivation analysis that H1N1 and MVA showed the highest stability against alcohol-based inactivation, with higher concentrations of WHO formulation I and II being required compared with CoVs, ZIKV, and EBOV. These results confirm MVA as the model surrogate virus for all enveloped viruses for testing chemical disinfectants and antiseptics in human medicine [8] . When testing nonenveloped viruses like noro-, polio-, or adenovirus, a far higher level of resistance to both WHO formulations was observed, probably due to the more hydrophilic character of these viruses [3, 6] . Interestingly, WHO formulation I was superior compared with WHO formulation II in inactivating these nonenveloped viruses, whereas in this study the opposite effect occurred, with WHO formulation II showing a higher virucidal activity against enveloped viruses. This discrepancy can be explained by the presence of the virus envelope, which likely renders enveloped viruses more susceptible to the isopropanol-based WHO formulation II compared with the ethanol-based WHO formulation I [14] . Furthermore, isopropanol has 1 more carbon than ethanol, giving it greater lipophilic properties and higher virucidal activities against lipophilic viruses [15] .