There is an urgent need for evidence-based development and implementation of engineering controls to reduce transmission of SARS-CoV-2, the etiological agent of COVID-19. Ultraviolet (UV) light can inactivate coronaviruses, but the practicality of UV light as an engineering control in public spaces is limited by the hazardous nature of conventional UV lamps, which are Mercury (Hg)-based and emit a peak wavelength (254 nm) that penetrates human skin and is carcinogenic. Recent advances in the development and production of Krypton Chlorine (KrCl) excimer lamps hold promise in this regard, as these emit a shorter peak wavelength (222 nm) and are recently being produced to filter out emission above 240 nm. However, the disinfection kinetics of KrCl UV excimer lamps against SARS-CoV-2 are unknown. Here we provide the first dose response report for SARS-CoV-2 exposed to a commercial filtered KrCl excimer light source emitting primarily 222 nm UV light (UV222), using multiple assays of SARS-CoV-2 viability. Plaque infectivity assays demonstrate the pseudo-first order rate constant of SARS-CoV-2 reduction of infectivity to host cells to be 0.64 cm2/mJ (R2 = 0.95), which equates to a D90 (dose for 1 log10 or 90% inactivation) of 1.6 mJ/cm2. Through RT-qPCR assays targeting the nucleocapsid (N) gene with a short (<100 bp) and long (~1000 bp) amplicon in samples immediately after UV222 exposure, the reduction of ability to amplify indicated an approximately 10% contribution of N gene damage to disinfection kinetics. Through ELISA assay targeting the N protein in samples immediately after UV222 exposure, we found no dose response of the ability to damage the N protein. In both qPCR assays and the ELISA assay of viral outgrowth supernatants collected 3 days after incubation of untreated and UV222 treated SARS-CoV-2, molecular damage rate constants were similar, but lower than disinfection rate constants. These data provide quantitative evidence for UV222 doses required to disinfect SARS-CoV-2 in aqueous solution that can be used to develop further understanding of disinfection in air, and to inform decisions about implementing UV222 for preventing transmission of COVID19.

There is an urgent need for evidence-based engineering controls to reduce transmission of SARS-CoV-2, which causes COVID-19. Although ultraviolet (UV) light is known to inactivate coronaviruses, conventional UV lamps contain toxic mercury and emit wavelengths (254 nm) that are more hazardous to humans than krypton chlorine excimer lamps emitting 222 nm (UV222). Here we used culture and molecular assays to provide the first dose response for SARS-CoV-2 solution exposed to UV222. Culture assays (plaque infectivity to Vero host) demonstrated more than 99.99% disinfection of SARS-CoV-2 after a UV222 dose of 8 mJ/cm2 (pseudo-first order rate constant = 0.64 cm2/mJ). Immediately after UV222 treatment, RT-qPCR assays targeting the nucleocapsid (N) gene demonstrated ~ 10% contribution of N gene damage to disinfection kinetics, and an ELISA assay targeting the N protein demonstrated no contribution of N protein damage to disinfection kinetics. Molecular results suggest other gene and protein damage contributed more to disinfection. After 3 days incubation with host cells, RT-qPCR and ELISA kinetics of UV222 treated SARS-CoV-2 were similar to culture kinetics, suggesting validity of using molecular assays to measure UV disinfection without culture. These data provide quantitative disinfection kinetics which can inform implementation of UV222 for preventing transmission of COVID-19.

SARS-CoV-2 (CoV2) infected, asymptomatic individuals are an important contributor to COVID transmission. CoV2-specific immunoglobulin (Ig), as generated by the immune system following infection or vaccination, has helped limit CoV2 transmission from asymptomatic individuals to susceptible populations (e.g. elderly). Here, we describe the relationships between COVID incidence and CoV2 lineage, viral load, saliva Ig levels (CoV2-specific IgM, IgA and IgG) and inhibitory capacity in asymptomatic individuals between Jan 2021 and May 2022. These data were generated as part of a large university COVID monitoring program and demonstrate that COVID incidence among asymptomatic individuals occurred in waves which mirrored those in surrounding regions, with saliva CoV2 viral loads becoming progressively higher in our community until vaccine mandates were established. Among the unvaccinated, infection with each CoV2 lineage (pre-Omicron) resulted in saliva Spike-specific IgM, IgA and IgG responses, the latter increasing significantly post-infection and being more pronounced than N-specific IgG responses. Vaccination resulted in significantly higher Spike-specific IgG levels compared to unvaccinated infected individuals, and uninfected vaccinees saliva was more capable of inhibiting Spike function. Vaccinees with breakthrough Delta infections had Spike-specific IgG levels comparable to those of uninfected vaccinees; however, their ability to inhibit Spike binding was diminished. These data demonstrate that COVID vaccines achieved hoped-for effects in our community, including the generation of mucosal antibodies that inhibit Spike and lower community viral loads, and suggest breakthrough Delta infections were not due to an absence of vaccine-elicited Ig, but instead limited Spike binding activity in the face of high community viral loads.