UV, ozone, and COVID-19 transmission in Ontario, Canada using generalised linear models

Quantifying the impact of environmental factors on COVID-19 transmission is crucial in preventing more cases. Ultraviolet (UV) radiation and ozone (O₃) have reported antimicrobial properties but few studies have examined associations with community infectivity of COVID-19. Research suggests UV light can be preventative while the effect of O₃ is contested. We sought to determine the relationship between UV, O₃, and COVID-19 incidence in Ontario, Canada.

In our time series analyses, we calculated daily incidence rates and reproductive number (R_t) from 34,975 cases between January and June 2020 across 34 Ontario Public Health Units. We used generalised linear models, adjusting for potential confounders, to calculate point estimates (PE) and 95% confidence intervals (CI) for UV and O₃. Analyses were further stratified by age groups and outbreaks at institutions versus community.

We found that 1-week averaged UV was significantly associated with a 13% decrease (95% CI: 0.80-0.96) in overall COVID-19 R_t, per unit increase. A negative association with UV was also significant among community outbreaks (PE: 0.88, 95% CI: 0.81-0.96) but not institutional outbreaks (PE: 0.94, 95% CI: 0.85-1.03). A positive association of O₃ with COVID-19 incidence is strongly suggested among institutional outbreak cases (PE: 1.06, 95% CI: 1.00-1.13).

Our study found evidence to support the hypothesis that higher UV reduced transmission of COVID-19 and some evidence that ground-level O₃ positively influenced COVID-19 transmission. Setting of infection should be strongly considered as a factor in future research. UV and O₃ may explain some of COVID-19's seasonal behaviour.