April 13 (UPI) -- U.S. health regulators on Tuesday recommended an immediate pause in the use of the Johnson & Johnson COVID-19 vaccine after several reported cases of blood clotting.
The Centers for Disease Control and Prevention and Food and Drug Administration made the recommendation after six women reported clotting issues.
"All six cases occurred among women between the ages of 18 and 48, and symptoms occurred 6 to 13 days after vaccination," the agencies said in a joint statement.
"In these cases, a type of blood clot called cerebral venous sinus thrombosis (CVST) was seen in combination with low levels of blood platelets (thrombocytopenia).
"We are recommending a pause in the use of this vaccine out of an abundance of caution."
One woman who developed clotting died, and another in Nebraska was hospitalized in critical condition, The New York Times reported.
White House COVID-19 response coordinator Jeff Zients and Dr. Anthony Fauci, chief medical adviser to President Joe Biden, explained the decision to pause the vaccine during a news conference, saying it will allow scientists to investigate the cases to gain a better understanding of the issue.
"We want the agencies to lead by science," Zients said.
Fauci said the blood clots are a rare event, "less than one in a million." Learning more about them will help doctors respond to the problem, which can be made worse by traditional treatment.
Those who have received the vaccine in the past two weeks should watch for symptoms such as headaches, shortness of breath and chest discomfort, Fauci said. He expects the pause to last days to weeks.
"We are aware of an extremely rare disorder involving people with blood clots in combination with low platelets in a small number of individuals who have received our COVID-19 vaccine," Johnson & Johnson said in a statement.
"In addition, we have been reviewing these cases with European health authorities. We have made the decision to proactively delay the rollout of our vaccine in Europe."
About 7 million doses of the vaccine, manufactured by Johnson & Johnson subsidiary Janssen, have been administered in the United States, the agencies said.
Adverse reactions from the vaccine appear to be extremely rare, according to the joint statement.
The federal government is expected to pause use of the vaccine at all federally run vaccination sites.
"[This pause] will not have a significant impact on our vaccination plan: Johnson & Johnson vaccine makes up less than 5% of the recorded shots in arms in the United States to date," Zients said in a statement. "The United States has secured enough Pfizer and Moderna doses for 300 million Americans.
"We are working now with our state and federal partners to get anyone scheduled for a J&J vaccine quickly rescheduled for a Pfizer or Moderna vaccine."
Last month, regulators in Europe called for a similar pause with administration of AstraZeneca's coronavirus vaccine in older adults, also due to reported cases of blood clotting. The European Union's top drug regulator said last week there's a possible link between the vaccine and the clotting cases.
The AstraZeneca vaccine has not been approved for use in the United States.