Without a vaccine for Covid-19, health care and other frontline workers must rely on personal protective equipment (PPE) to guard themselves from exposure to the novel coronavirus. Demand for PPE has been substantial in Massachusetts since the outbreak began. What’s unclear is just how great the demand will remain going forward, and if the state is equipped to meet it. To help settle this uncertainty, MIT Lincoln Laboratory conducted a study to estimate demand for PPE in Massachusetts over the next 18 months, specifically for N95 and surgical masks, gloves,…