The first trucks carrying a COVID-19 vaccine for widespread use in the United States are getting ready to roll out of a Michigan manufacturing plant. The shipments Sunday morning will set in motion the biggest vaccination effort in American history. The shots that are critical to stopping the nation’s coronavirus outbreak are destined to reach states a day later. Initial doses of the Pfizer vaccine will be likely be limited to health workers and nursing home residents. The Food and Drug Administration authorized emergency use of the vaccine Friday, saying it is highly protective and presents no major safety issues.