WASHINGTON (AP/WTNH) — The U.S. is recommending a “pause” Tuesday in the administration of the single-dose Johnson & Johnson COVID-19 vaccine to investigate reports of potentially dangerous blood clots, according to a joint statement from the Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA).

In a statement obtained by ABC News, The CDC and FDA said they are reviewing data involving the J&J vaccine, in which a type of blood clot called cerebral venous sinus thrombosis (CVST) was seen in combination with low levels of blood platelets (thrombocytopenia).

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The statement said all six cases occurred among women between the ages of 18 and 48, and symptoms occurred six to 13 days after vaccination. 

The CDC is preparing a meeting of the Advisory Committee on Immunization Practices (ACIP) Wednesday to further review these findings. The FDA will also conduct a review. Until then, they both are recommending a pause in the use of the J&J vaccine out of an abundance of caution.

“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 joint statement said.

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During a news conference Tuesday morning, health officials emphasized that even though the events appear to be very rare, safety is key. They said they want to take the time to fully understand how and why the blood clots are happening.

For people who got the vaccine a month ago, they said there is a low concern. For those who recently got the vaccine, patients are asked to monitor their health and report any severe symptoms to a physician. Symptoms to watch for are headaches, abdominal pain, trouble breathing, leg pain and swelling; especially uneven swelling.

The FDA says the combination itself of CVST and thrombocytopenia found in the Johnson & Johnson vaccine-related blood clot cases were similar to the cases related to the AstraZeneca vaccine, which is being used in Europe.

Health officials said they have not found a combination of CVST and thrombocytopenia in patients who have received the Pfizer or Moderna vaccine.

ABC News has obtained a statement from Johnson & Johnson in response, saying,

“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.”

A spokesperson for CVS told ABC News, “We are immediately implementing a pause in the use of the Johnson and Johnson’s COVID-19 vaccine per the recommendation from federal health agencies.”

The Connecticut Department of Public Health also suggested a pause on the vaccine. They released the following statement:

Early this morning, the U.S. FDA and CDC issued a joint statement recommending a pause on the use of the Johnson & Johnson (J&J) COVID-19 vaccine following six reported US cases of a rare blood clotting event. Although these events are rare, and none have occurred in Connecticut, the Connecticut Department of Public Health recommends that COVID vaccine providers pause on administration of J&J vaccine for the time being while the FDA and CDC complete their review.

Connecticut leaders are echoing the importance of safety; Bridgeport Mayor Joe Ganim released a statement Tuesday saying,

“Safety and confidence in the vaccine is paramount. Unless, or until we are 100% confident in the J & J vaccine, we will pause its use.” 

The City of New Haven, in partnership with Griffin Hospital, postponed the scheduled mobile clinics for Tuesday, April 13, following the update. The clinic will reopen Wednesday, April 14, using Moderna and Pfizer.

“Sit tight with J&J vaccine. I would like to think they are going to do their tests and get that out again in the very near future,” advised Governor Ned Lamont.

Connecticut’s vaccine supply does not rely on the Johnson & Johnson doses. A small portion, about 11%, of the state’s supply this week was going to be the J&J.

100,000 Connecticut residents have received the vaccine.

“These are six reported cases out of 7 million subjects who have received the Johnson and Johnson vaccine. I think that number by itself represents the really few patients who ended up getting the getting the blood clots — so I think that’s an important point to consider,” Dr. Hyung Chun, Cardiologist & Associate Professor of Medicine, Yale School of Medicine.

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Hartford HealthCare said it has halted the use of the Johnson & Johnson vaccine, following the guidance of the FDA and CDC. Hartford HealthCare has provided 18,857 vaccinations using J&J as of Tuesday morning.

As of April 12, more than 6.8 million doses of the J&J vaccines have been administered in the U.S.

Anyone experiencing severe side effects from any COVID vaccine is asked to visit the VAERS website to report any adverse events.

The state will have more information on how they’re handling second-dose appointments for mobile clinics in the coming days. Despite the “curveball” with this “pause,” state officials believe they’ll be able to stay on track hitting vaccination goals.

In the meantime, 15 mobile vans will now have Pfizer and Moderna on board. Appointments are still available.

Josh Geballe the Chief Operating Officer said, “Key message here if you are looking for a vaccine appointment get online or call. You should be able to get one quickly.”

Supply is starting to outpace demand — experts predicted that would happen by the end of April. Right now, the state is still getting J&J deliveries but is just hanging on to them.