(CNN) As health officials discussed how to handle reports of blood clots possibly linked to Johnson & Johnson's Covid-19 vaccine, one option considered was issuing a warning to health care providers without recommending a full pause, multiple sources told CNN.
But as officials discussed the best path forward during a Zoom call on April 12, they decided recommending a full pause would be necessary because four of the women had been treated with the anticoagulant drug heparin. The rare type of blood clots observed in these cases require unique treatment and heparin should not be used to treat these types of blood clots, according to doctors and health officials.
The US Food and Drug Administration officials are now waiting for a Friday meeting with the US Centers for Disease Control and Prevention's vaccine advisory committee before taking any more steps.
The CDC and FDA last week recommended that the United States pause the use of Johnson & Johnson's Covid-19 vaccine over six reported US cases -- all of which were in women between the ages of 18 and 48 -- of a "rare and severe" type of blood clot. The six reported cases were among more than 6.8 million doses of the Johnson & Johnson vaccine administered in the United States.
White House Covid-19 response coordinator Jeff Zients stressed last week that the pause in the Johnson & Johnson vaccine would "not have a significant impact" on the current pace of vaccinations in the US. He said there was "more than enough" supply of the Pfizer/BioNTech and Moderna Covid-19 vaccines, which were also granted emergency use authorization by the FDA.
Zients argued the pause in the J&J vaccine should "give the American people confidence in the FDA and CDC, the thoroughness of the review process, and their commitment to transparency and protection of public health."
"We believe that by empowering Americans with data and facts, we will strengthen the public's trust in government, and increase their confidence in the vaccine," Zients said. He emphasized that building vaccine confidence is central to the administration's efforts to vaccinate the country.
Dr. Anthony Fauci, Biden's chief medical adviser and the director of the National Institute of Allergy and Infectious Diseases, noted last week during a White House briefing that the cases amount to "less than 1 in a million."
Fauci told CNN last week that he believes the pause should "underscore and confirm how seriously we take safety, even though it's a very rare event."
"If anyone's got a doubt that they may not be taking safety very seriously, I think this is an affirmation that safety is a primary consideration when it comes to the FDA and the CDC," he said. "That's why it was done and that's why it's a pause. It isn't a cancellation; it's a pause."
National Institutes of Health Director Dr. Francis Collins said last week that the pause on the Johnson & Johnson vaccine would allow researchers to investigate a potential link to severe blood clotting events, particularly whether certain types of people are more susceptible.
Collins noted that all six of the reported cases were among women and the pause would allow researchers to investigate whether particular populations are more susceptible and should perhaps not take the vaccine.
This story has been updated with additional information.