Credit: Unsplash/CC0 Public Domain Good caregivers are often in short supply, but after the COVID-19 pandemic hit the U.S. in early 2020, staff levels at nursing homes dropped by 10%. What was a simple personnel shortage has moved closer to being a nursing-care crisis. "We have an aging population, care for them is labor-intensive, and there are shortages everywhere in that supply chain," says MIT economist Jonathan Gruber. As it happens, about one-fifth of health care support workers in the U.S. are immigrants. And as a newly published study of the nation's metro areas shows, changes in immigration levels can affect how much nursing care the elderly receive. "When immigration rises in a city, it significantly increases the health care workforce," says Gruber, co-author of the study and a paper detailing its findings.…