UV-C Light Completely Blocks Aerosol Transmission of Highly Contagious SARS-CoV-2 Variants WA1 and Delta in Hamsters

Abstract

Behavioral and medical control measures have not been effective in containing the spread of SARS-CoV-2 in large part due to the unwillingness of populations to adhere to "best practices". Ultraviolet light with wavelengths of between 200 and 280 nm (UV-C) and, in particular, germicidal ultraviolet light, which refers to wavelengths around 254 nm, have the potential to unobtrusively reduce the risk of SARS-CoV-2 transmission in enclosed spaces. We investigated the effectiveness of a strategy using UV-C light to prevent airborne transmission of the virus in a hamster model. Treatment of environmental air with 254 nm UV-C light prevented transmission of SARS-CoV-2 between individuals in a model using highly susceptible Syrian golden hamsters. The prevention of transmission of SARS-CoV-2 in a natural system by treating elements of the surrounding environment is one more weapon in the arsenal to combat COVID. The results presented indicate that coupling mitigation strategies utilizing UV-C light, along with current methods to reduce transmission risk, have the potential to allow a return to normal indoor activities.

Keywords: COVID19; SARS-CoV-2; UV-C; aerosol; hamster; transmission.

Figure 1

UV fluence measurements (mJ/cm²). UV-C light incidence at 254 nm at four points along the length of the quartz tube at 20 cm intervals starting 1 cm from the UV-C containment box exit. Measurements were made with a UV-C meter type X1-1-UV-3725 measurement system, comprising a X1–5 optometer with a UV-3725-5 detector head, calibrated for narrow band sources such as LP mercury lamps. After a 1-hour lamp warmup, irradiance measurements (mW/cm²) were taken in triplicate with the sensor facing (1) the UV-C light source (top), (2) away from the UV-C light source (bottom), (3) the right side of the box, and (4) the left side of the box. These irradiance dose measurements were used to calculate the total UV-C incidence dose (mJ/cm²) along the length of the tube by multiplying irradiance dose by exposure time. The diagram shows the positions that the measurements were taken from and the placement of the senser in the tube at 1 cm.

Figure 2

Experimental aerosol transmission with the UV-C irradiation setup. Two cages are separated with a 1250 mm × 73 mm i.d. tube. The center portion of the tube is 662 mm of UV transparent quartz surrounded by a HDPE box housing a UV-C light source. Two donor hamsters, infected intranasally with 8 × 10⁴ TCID₅₀ SARS-CoV-2 of either lineage A or the Delta variant 1 day prior to the experiment, were placed in the upstream cage, and two naïve sentinel hamsters were placed in the downstream cage with a 934.5 L/h airflow for 4 h. The arrow indicates the direction of the airflow.

Figure 3

UV-C irradiation blocks SARS-CoV-2 aerosol transmission in hamsters. (A,B) Boxplot (minimum to maximum) of genomicRNA and subgenomicRNA Lineage A SARS-CoV-2 RNA in oropharyngeal swabs collected on 1-, 2-, and 3-days post exposure. Blue dots represent the no UV-C treatment group (n = 8), and gray dots represent the UV-C treatment group (n = 8). (C,D) Boxplot (minimum to maximum) of genomicRNA and subgenomicRNA Delta SARS-CoV-2 RNA in oropharyngeal swabs collected on 1-, 2-, and 3-days post exposure. Pink dots represent the no UV-C treatment group (n = 8), and light-blue dots represent the UV-C treatment group (n = 8). Dotted line = limit of detection.