Johnson and Johnson

About 7 million people have received the single-shot vaccine in the United States. And out of those people, six have reportedly experienced cerebral venous sinus thrombosis (CVST) blood clots as of Tuesday morning. "Right now, these adverse events appear to be extremely rare," the agencies added.

Wake County announced Thursday evening that it stopped administering Johnson & Johnson doses at PNC Arena after 18 of the more than 2,300 people vaccinated experienced adverse reactions. People at the site were given the option of the Pfizer vaccine or allowed to reschedule their existing J&J appointments, according to officials.

The healthcare product manufacturer said that in the U.S. and seven other countries the single-dose vaccine was shown to be 66% effective against moderate and severe cases of COVID-19, and up to 85% against patients with near-death symptoms.