Face masks and coverings are not 100% effective at preventing the spread of the coronavirus, according to a September study from the US Centers for Disease Control and Prevention (CDC).The study, conducted in July, found that over 70% of the 154 "case-patients," who had tested positive for COVID-19, were infected despite making efforts to abide by CDC guidelines, including the wearing of face masks. It is possible that some of the infections may have been caused by removing face coverings for food or drink. Another possibility is airflow, as “direction, ventilation and intensity of airflow might affect virus transmission, even if social distancing measures and mask use are implemented according to current guidance,” according to the CDC report.This is reflective of an incident at Tel Aviv's Sourasky Medical Center, where a doctor and two nurses may have been infected with the coronavirus by the aerosol coming from a ventilator being used on a patient.However, the CDC report further explained that it is impossible to evaluate exactly where someone contracted the virus.“Characterization of community exposures can be difficult to assess when widespread transmission is occurring, especially from asymptomatic persons within inherently interconnected communities,” the report stated.Infection with COVID-19 despite wearing protective measures has been recorded, with even medical professionals equipped with maximal personal protective equipment (PPE) occasionally contracting the virus.Despite this, face masks are still shown to be the most effective means of slowing the spread of the virus, and medical bodies worldwide recommend wearing them and maintaining social distancing measures.Also, Facebook fact-checker reviewed this study and was able to highlight some flaws:"The comparison made in the claim cannot evaluate mask effectiveness in reducing the spread of COVID-19, because the study that the claim is based on included many more people who wear masks than people who didn’t," the fact-checker. "Of the 314 individuals surveyed in the study, only 11 never wore masks. Because the group sizes are so uneven, a comparison of the proportion of people who tested positive for COVID-19 who wore masks and who didn’t would show mask wearers to be the majority."