On a snowy January morning, Luis Portillo stood in line on the side of a busy road in Silver Spring, Maryland — a suburb just north of Washington, D.C. — with about 200 other people, waiting for his turn to get tested for covid-19 at Mary’s Center, a federally qualified health center. Portillo, a 65-year-old bakery worker originally from El Salvador, jammed his hands in his coat pockets and shivered in the 25-degree weather. Though Portillo is not particularly concerned about covid — he is vaccinated and boosted and had a mild case last year — he came out because it’s necessary to “look after …