UCLA

Background: Long-term exposure to fine particulate matter (PM2.5) is an established risk factor for many adverse health outcomes via different mechanisms, and thus predisposes individuals and populations to elevated risks of both infectious and chronic health outcomes. Previous studies reported the association between PM2.5 exposure and COVID-19 outcomes based on arbitrarily cut-off points. This study investigated this association during the first two surges of the pandemic and examined whether non-pharmacologic prevention initiatives might intervene this association. In addition, though vaccines against SARS-CoV-2 were safe and effective, its community-wide impacts on reducing COVID-19 incidence and mortality corresponding to the predominant strain in the population have not yet been studied. Lastly, we aim to confirm the association between PM2.5 and lung cancer susceptibility in Los Angeles, as well as addressing whether PM2.5 is associated with UADT cancers susceptibility, which have been understudied. Objective and Specific Aims: We aimed to evaluate the association between ambient PM2.5 exposure and COVID-19 incidence and lung and UADT cancer susceptibility. The specific aims were: (1) to estimate the association between long-term exposure to ambient PM2.5, facemask mandates, stay home orders and COVID-19 incidence in the United States during the first two surges; (2) to estimate the association between SARS-CoV-2 vaccines coverage and COVID-19 incidence and mortality in the United States during the Alpha, Delta, and Omicron predominance; and (3) to estimate the association between long-term exposure to ambient and indoor PM2.5 and lung and UADT cancers susceptibility. Study Design and Population: For Specific Aims 1 and 2, we employed a nation-wide ecologic study design, including more than 3,000 counties in the US. Analyses were conducted to estimate the associations between ambient PM2.5, non-pharmacologic prevention initiatives, including facemask mandates and stay-home policies, and vaccination coverage at the county-level and COVID-19 incidence and mortality. The study utilized publicly available data. In Specific Aim 3, we aimed to estimate the association between air pollution and susceptibility of lung and UADT cancers, using a population-based case-control study in the Los Angeles County. The study included 577 lung cancer cases, 565 UADT cancers cases, and 983 controls after applying exclusion criteria. Statistical Methods: For Specific Aim 1, we fit negative binomial models to assess COVID-19 incidence in association with PM2.5 and policies during the first two surges of SARS-CoV-2 pandemic, as of September 12th, 2020. Stratified analyses by facemask policy and stay home policy were also performed. For Specific Aim 2, generalized estimating equations were used to estimate associations between US county-level cumulative complete vaccination rates and booster distribution and the daily change in county-wide COVID-19 risks and mortality during Alpha (April 23rd – July 2nd, 2021), Delta (July 3rd – December 1st, 2021) and Omicron (December 2nd, 2021 – March 25th, 2022) predominance. For both Aims, models were adjusted for potential confounders at both county and state level. A 2-week lag and a 4-week lag were introduced to assess vaccination rates impact on incidence and mortality, respectively. For Specific Aim 3, unconditional logistic regressions were applied to estimate the association between air pollution, including ambient PM2.5 one-year before diagnosis, exposure to household air pollution, and an air pollution index, and lung and UADT cancers’ susceptibility, adjusting for potential confounders. Results: For Aim 1, after adjusting for county-level and state-level potential confounders, each 1-�g/m3 increase in annual average concentration of PM2.5 exposure was associated with an increase in COVID-19 risk (relative risk (RR) = 1.0756, 95% CI: 1.0376, 1.1149). Facemask mandates and stay home policies were inversely associated with COVID-19 with adjusted RRs of 0.8466 (95% CI: 0.7598, 0.9432) and 0.9193 (95% CI: 0.8021, 1.0537), respectively. The associations between PM2.5 and COVID-19 were consistent among counties with or without preventive policies. For Aim 2, among 3,073 counties in 48 states, the average county population complete vaccination rates of all age groups were 50.79% as of March 11th, 2022. Each percentage increase in vaccination rates was associated with reduction of 4% (RR = 0.9607, 95% CI: 0.9553, 0.9661) and 3% (RR = 0.9694, 95% CI: 0.9653, 0.9736) in county-wide COVID-19 cases and mortality, respectively, when Alpha was the dominant variant and after adjusting for potential confounders. The associations between county-level vaccine rates and COVID-19 incidence diminished during the Delta (RR = 0.9988, 95% CI: 0.9964, 1.0011) and Omicron (RR = 0.9969, 95% CI: 0.9919, 1.0019) predominance. Vaccination coverage was associated with slightly decreased COVID-19 mortality (RR = 0.9934, 95% CI: 0.9889, 0.9980) when Delta was the most prevalent strain, but with a marginal increase in COVID-19 mortality (RR = 1.0061, 95% CI: 1.0022, 1.0101) when Omicron was circulating. During the Omicron predominance, each percent increase in people receiving a booster shot was associated with reduction of 6% (RR = 0.9356, 95% CI: 0.9235, 0.9479) and 4% (RR = 0.9595, 95% CI: 0.9431, 0.9761) in COVID-19 incidence and mortality in the community, respectively. For Specific Aim 3, each 1-�g/m3 increase in ambient PM2.5 one-year before diagnosis was associated with elevated risks in lung (odds ratio (OR) = 1.02, 95% CI: 0.98, 1.06) and UADT (OR = 1.04, 95% CI: 1.00, 1.09) cancers susceptibility, adjusting potential confounding factors. Conclusions and public health implications: These results add evidence to the associations between PM2.5 with COVID-19 incidence and with lung and UADT cancers susceptibility. Thus, our results underscore the health hazards associated with increased ambient PM2.5 and may be informative for policymaking and program planning for continuing to improve air quality. Moreover, the non-pharmacologic prevention initiatives and increasing vaccination coverage are shown to be effective in reducing COVID-19 incidence and mortality during different outbreaks of the SARS-CoV-2 variants, indicating both NPIs and vaccination are essential decisions in better preparation for the next surge of COVID-19 and even for the next emerging pandemic in the future.