https://www.medscape.com/viewarticle/984992#vp_1
Medical Masks Versus N95 Respirators for Preventing COVID-19 Among Health Care Workers : A Randomized Trial – PubMed (nih.gov)
“The confidence intervals around this, that is, what the possible results could be if the trial was repeated many times, range from −2.5% to 4.9%,” he told Medscape. “This means that the risk of a COVID-19 infection in those using the medical masks could have ranged from anywhere from 2.5% reduction in risk to a 4.9% increase in risk. Readers and policy makers can decide for themselves about this.”
Dr. Shepherd opinion —- A CI that crosses zero typically means that the predictor has NO relationship with the response. The study did not, likely, have enough subjects to determine if there is a causal relationship. In this case, I would not change my opinion or practice based on this study.