Johnson & Johnson’s Chinese Communist Party (CCP) Virus or COVID-19 vaccination program is being paused under a U.S. health officials’ recommendation made on Tuesday, April 13 until an investigation into cases of post-vaccination blood clots is completed.

Officials told reporters in a call that 7.2 million doses of the J&J vaccine had been administered in the United States as of April 13. Six cases, all women, suffered a rare and severe form of clot called cerebral venous sinus thrombosis (CVST) combined with low blood platelet levels.

According to the Food and Drug Administration (FDA), one of the patients died, and another is in critical condition in the hospital. The patients, who range in age from 18 to 48, developed symptoms 6-13 days after receiving the Johnson & Johnson vaccine.

Immunology experts agreed with U.S. officials that the Johnson & Johnson vaccine appeared to pose an exceptionally low risk.

“Right now, these adverse events appear to be extremely rare,” Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said on the call.

Dr. Amesh Adalja, an infectious disease specialist at the Johns Hopkins Center for Health Security, was concerned that the pause would raise people’s apprehension about getting vaccinated. He said in an email, “Even if causally linked to the vaccine: 6 cases with about 7 million doses … is not something to panic about,” indicating that the risk appears to be lower than that of oral contraceptive clots.

Dr. Mark Rupp, chief of the University of Nebraska Medical Center’s Division of Infectious Diseases, told reporters in a  Zoom call, “The pause is appropriate, and it’s obviously being done to be very careful, to be very prudent, to carefully examine these cases for a possible association with the vaccine. It’s a demonstration that the Vaccine Adverse Event Reporting System (VAERS) really is working.”

In Europe, the regulators have also found a possible link between AstraZeneca’s COVID-19 vaccine and a similar rare blood clotting problem that led to a small number of deaths. The European Medicines Agency said that 169 cases of CVST and 53 of splanchnic vein thrombosis had been reported as of April 4 after vaccination with the AstraZeneca shot. About 34 million people had been given the shot in Europe by then.

FDA official Peter Marks said it was “plainly obvious” the Johnson & Johnson cases were “very similar” to the AstraZeneca ones. He added that no related blood clot cases had been identified among recipients of the Moderna or Pfizer/BioNTech vaccines, which both use different technology and account for the vast majority of vaccinations in the United States to date.

On Wednesday, an advisory committee of the U.S. Centers for Disease Control and Prevention (CDC) will study the clotting cases and vote on guidelines for future use of the Johnson & Johnson vaccine. The FDA will then review the analysis.

“While these events are very rare, we’re recommending a pause in the use of the J&J COVID-19 vaccine to prepare the health care system, to recognize and treat patients appropriately, and to report severe events they may be seeing in people who’ve received the J&J vaccine,” said Dr. Anne Schuchat, principal deputy director of the CDC.

The pause, according to White House officials, would not affect the government’s vaccination schedule.

The White House said that appointments for the Johnson & Johnson shot were being rescheduled around the country to obtain the other two approved vaccines. There is enough supply of Pfizer and Moderna shots to meet President Joe Biden’s target of administering 200 million shots during his first 100 days in office.

The FDA advised patients to monitor for symptoms such as severe headaches, abdominal pain, leg pain, or shortness of breath for up to three weeks. Dizziness, lightheadedness, and sweating symptoms were among the adverse effects, according to a CDC spokesperson.