After a series of reports of blood clots linked to the Johnson & Johnson (JNJ) COVID vaccine, the Food and Drug Administration and the Centers for Disease Control and Prevention have recommended that the use of shot be paused “out of an abundance of caution.”

The agencies made the announcement Tuesday after reports of six cases of blood clots following the single-dose shot of the Johnson & Johnson vaccine.

The FDA said the side effect is a rare and severe type of blood clot called cerebral venous sinus thrombosis that was seen in combination with low levels of blood platelets.

All six cases occurred in women aged 18 to 48, with symptoms occurring six to 13 days after vaccination of the Johnson & Johnson vaccine. Because of the type of blood clot, typical treatment of an anticoagulant drug such as heparin may be dangerous, and alternative treatment may be needed, according to the agency.

To date, more than 6.8 million doses of the Johnson & Johnson COVID vaccine have been administered to the American public, making the reported cases of blood clots a one-in-a-million occurance to date. The Johnson & Johnson vaccine is said to have up to 66% effectiveness against COVID-19.

The CDC will convene a meeting of the Advisory Committee on Immunization Practices on Wednesday to further review the patients' cases, while the FDA will review that analysis as it investigates the cases. The agencies said until that process is complete, it is recommending the use of Johnson & Johnson’s vaccine be paused.

“This is important, in part, to ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot,” the FDA said in a statement.

In a statement obtained by ABC News, following the announcement from the FDA and the CDC, Johnson & Johnson said: “The safety and well-being of the people who use our products is our number one priority. We share all adverse event reports about individuals receiving our COVID-19 vaccine, along with our assessment of these reports, with health authorities in compliance with regulatory standards

“We are aware that thromboembolic events including those with thrombocytopenia have been reported with COVID-19 vaccines. At present, no clear causal relationship has been established between these rare events and the Janssen COVID-19 vaccine. We continue to work closely with experts and regulators to assess the data and support the open communication of this information to healthcare professionals and the public.”

While the FDA said the blood clots appear to be “extremely rare,” COVID vaccine safety is its top priority. The FDA said it takes take the reports of health problems related to the vaccine seriously.

The FDA said it has received other reports about symptoms from the Johnson & Johnson vaccine that include severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination. Anyone experiencing these symptoms should contact their healthcare provider.

More information will be provided by the FDA and CDC during a media briefing at 10 a.m. Tuesday.

Over 74 million people have been fully vaccinated to date, with one of the three vaccines –- Pfizer, Moderna, or Johnson & Johnson -- available to the American public, the CDC said.-

Shares of Johnson & Johnson were trading at $157.05 as of premarket hours, down $4.59 or 2.84%.

Johnson & Johnson Vaccine Vials of a COVID-19 Vaccine are pictured with the logo of US pharmaceutical company Johnson & Johnson on November 17, 2020. Photo: Justin Tallis/AFP via Getty Images