Impact on Transmissibility and Case Fatality Rate of COVID-19 of the Mandatory Face Shield Use in Addition to Mask during the Pandemic: The Philippine Experience.

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, R 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.