WASHINGTON (AP) — The U.S. recommendation to  “pause” use of the single-dose Johnson & Johnson COVID-19 vaccine set off a chain reaction worldwide and dealt a setback to the global vaccine campaign. The Centers for Disease Control and Prevention and the Food and Drug Administration announced that they were investigating unusual clots that occurred 6 to 13 days after vaccination. The acting FDA commissioner says she expects the pause to last a matter of days. The decision triggered swift action in Europe and elsewhere as regulators moved to halt the use of the J&J vaccine, at least for now. Hundreds of thousands of doses of the vaccine were due to arrive in European countries this week.