The U.S. capacity for SARS-CoV-2 testing is limited by several items, including the swabs used to collect patient specimens, but the supply of reagents has been front and center recently. Despite those concerns, several private test makers said they are quickly ramping up production, including Thermo Fisher Scientific Inc., of Waltham, Mass., which said it has enough supplies of all types on hand to provide 2 million reactions per week, a volume that should increase to 5 million per week in April.