The FDA and CDC announced that they are calling for an immediate pause on the use of the single-dose Johnson & Johnson vaccine following the emergence of a rare blood clotting in six recipients.

The blood clots developed in six women between the ages of 18 and 48 within one to three weeks of receiving the Johnson & Johnson vaccination. One woman died and a second woman in Nebraska has been hospitalized in critical condition. More than 6.8 million doses of the Johnson & Johnson vaccine have been administered in the United States, while an additional nine million doses shipped out to the U.S., according to the CDC.

While safety issues are examined, officials will temporarily stop using the vaccine at federal sites and are urging states to follow their lead. Pharmacy giants such as CVS and Walgreens that participate in a federal vaccination program, as well as the U.S. military, have stopped administering the Johnson & Johnson vaccine.

Johnson & Johnson issued a statement that noted the company’s decision to “proactively delay the rollout” of its vaccine in Europe. Despite this action, the company stated that there is currently no clear causal relationship between this “extremely rare disorder” and the Janssen COVID-19 vaccine.

“We have been working closely with medical experts and health authorities, and we strongly support the open communication of this information to healthcare professionals and the public,” the statement said.

Despite this setback, White House COVID-19 response coordinator Jeff Zients remains confident that President Joe Biden will hit his goal of 200 million administered vaccine doses within his first 100 days in office.

“This announcement will not have a significant impact on our vaccination plan,” Zients said in a statement. “Johnson & Johnson vaccine makes up less than five percent of the recorded shots in arms in the United States to date.”

Recipients of the Johnson & Johnson shot who have developed severe headache, abdominal pain, leg pain or shortness of breath within three weeks after getting vaccinated should contact their health care provider, according to the statement.