At Mass General Brigham, the largest healthcare system in MA, an infection reduction strategy including masking and testing was implemented. Preintervention period: SARS-CoV-2 positivity rate increased from 0% to 21.32%. Intervention period: SARS-CoV-2 positivity rate decreased from 14.65% to 11.46%. Randomized trials during a pandemic aren't feasible, but results support universal masking as an important reduction strategy.