Summary Background Understanding factors impacting deaths from COVID‐19 is of the highest priority. Seasonal variation in environmental meteorological conditions affects the incidence of many infectious diseases and may also affect COVID‐19. Ultraviolet (UV) A (UVA) radiation induces release of cutaneous photolabile nitric oxide (NO) impacting the cardiovascular system and metabolic syndrome, both COVID‐19 risk factors. NO also inhibits the replication of SARS‐CoV2. Objectives To investigate the relationship between ambient UVA radiation and COVID‐19 deaths. Methods COVID‐19 deaths at the county level, across the USA, were modelled in a zero‐inflated negative‐binomial model with a random effect for states adjusting for confounding by demographic, socioeconomic and long‐term environmental variables. Only those areas where UVB was too low to induce significant cutaneous vitamin D3 synthesis were modelled. We used satellite‐derived estimates of UVA, UVB and temperature and relative humidity. Replication models were undertaken using comparable data for England and Italy. Results The mortality rate ratio (MRR) in the USA falls by 29% [95% confidence interval (CI) 40% to 15%) per 100 kJ m–2 increase in mean daily UVA. We replicated this in independent studies in Italy and England and estimate a pooled decline in MRR of 32% (95% CI 48% to 12%) per 100 kJ m–2 across the three studies. Conclusions Our analysis suggests that higher ambient UVA exposure is associated with lower COVID‐19‐specific mortality. Further research on the mechanism may indicate novel treatments. Optimized UVA exposure may have population health benefits.

Objectives To determine whether UVA exposure might be associated with COVID-19 deaths Design Ecological model and meta-analysis Setting 2,474 counties of the contiguous USA, 6,755 municipalities in Italy, 6,274 areas in England. Data were collected during their Vitamin D winter (monthly mean UVvitd of under 165 KJ/m2) from Jan to April 2020. Participants The at-risk population is the total county population, with measures to incorporate spatial infection into the model. The model is adjusted for: age, ethnicity, socioeconomic deprivation, long term PM2.5, and UV weighted by the vitamin D action spectrum. Main outcome measures We derive UVA measures for each area and estimate their relationship with COVID-19 mortality with a random effect for States, in a multilevel zero-inflated negative binomial model. In the USA and England death certificates had to record COVID-19. In Italy excess deaths in 2020 over expected from 2015-19. Data sources Satellite derived mean daily UVA dataset from Japan Aerospace Exploration Agency. Data on deaths compiled by Center for Disease Control (USA), Office for National Statistics (England) and Italian Institute of Statistics. Results Daily mean UVA (January-April 2020) varied between 450 to 1,000 KJ/m2 across the three countries. Our fully adjusted model showed an inverse correlation between UVA and COVID-19 mortality with a Mortality Risk Ratio (MRR) of 0.73 (0.62 to 0.87)per 100KJ/m2 increase UVA in the USA, 0.81 (0.71 to 0.93) in Italy and 0.51 (0.39 to 0.66) in England. Pooled MRR was 0.68 (0.53 to 0.66). Conclusions Our analysis, replicated in 3 independent national datasets, suggests ambient UVA exposure is associated with lower COVID-19 specific mortality. This effect is independent of vitamin D, as it occurred at irradiances below that likely to induce significant cutaneous vitamin D3 synthesis. Causal interpretations must be made cautiously in observational studies. Nonetheless this study suggests strategies for reduction of COVID-19 mortality