UCSF experts answer questions about Johnson & Johnson vaccine pause FacebookTwitterEmail This Dec. 2, 2020, photo provided by Johnson & Johnson shows vials of its COVID-19 vaccine in the United States.Associated Press You may have heard the news: The U.S. on Tuesday recommended a “pause” in using the single-dose Johnson & Johnson COVID-19 vaccine to study severe illness that developed in six American women out of the 6.8 million people who received doses across the country. The Centers for Disease Control and Prevention and the Food and Drug Administration announced that they were investigating unusual but potentially dangerous blood clots that occurred 6 to 13 days after vaccination. The acting FDA commissioner said she expected the pause to last a matter of days.