Background: While wearing face shields and other gears to protect the facial mucous membranes not covered by face masks are proven to decrease the odds of infection in the hospital setting, there is no concrete evidence of its efficacy in the general public. Objective: To determine the effectiveness of face shield use in the general public in the local setting. Methods: This study utilized an ecological study design, with the weeks when the policy was implemented serving as the exposure variable while the weeks when the policy was not in effect, whether prior to or after, serving as control. Primary outcomes were mean incidence of COVID-19 and case fatality rate (CFR) per week. Results: When the mandatory face shield use was implemented, the mean incidence of COVID-19 per week was higher compared to weeks when it was not implemented [93 cases per 1000 population per week (ptpw) vs 65 cases, relative risk:1.43, z=-3.79, p=0.0001]. Moreover, during weeks when only less than 50% of the population was vaccinated with first dose (93 cases ptpw vs 52 cases, RR: 1.79, z=-4.3, p<0.0001) and complete doses (93 cases ptpw vs 66 cases ptpw, RR:1.41, z=-3.69, p=0.0002), the mean incidence of COVID-19 per week were statistically higher in weeks when face shield use was in effect. Controlling the status of vaccination and the predominant strain, face shield use increased the incidence of COVID-19 cases ptpw by 38 (F=13, R2=39%, p=0.026) to 50 (F=3.06, R2=12.2%, p=0.032) compared to no face shield use. No difference in CFR between weeks with face shield use and no face shield use was seen (29 deaths ptpw vs 32 deaths per ptpw, p=1.0). Nevertheless, when the weeks with no vaccination (27 deaths ptpw vs 48 deaths ptpw, RR=0.56, p=0.0018), less than 50% of the population were vaccinated with f irst dose (30 deaths ptpw vs 50 deaths ptpw, RR:0.6, p=0.0005), and complete doses (30 deaths vs 47 deaths ptpw, RR:0.64, p=0.0042) were only considered, face shield use significantly decreased the mean CFR per week. Controlling the incidence rate of COVID-19, vaccination status, and prevalent strain, face shield use decreases the number of deaths by 26 per 1000 COVID-19 diagnosed cases (F=7.4, R2=28.3, p=0.010). Conclusions In general, although face shield use increased susceptibility to COVID-19, it decreased case fatality rate in the Philippines. However, a more robust and controlled study in the future may be needed to truly justify its recommendation for the public.
COVID-19 ; epidemiology ; public health ; Philippines