The reports appear similar to a rare, unusual type of clotting disorder that European authorities say is possibly linked to another COVID-19 vaccine not yet cleared in the U.S., from AstraZeneca.

More than 6.8 million doses of the J&J vaccine have been administered in the U.S., the vast majority with no or mild side effects.

U.S. federal distribution channels, including mass vaccination sites, will pause the use of the J&J shot, and states and other providers are expected to follow. The other two authorized vaccines, from Moderna and Pfizer, make up the vast share of COVID-19 shots administered in the U.S. and are not affected by the pause.

[ County-by-county guide: Here’s when, where you can get the COVID-19 vaccine ]

CDC’s Advisory Committee on Immunization Practices will meet Wednesday to discuss the cases and the FDA has also launched an investigation into the cause of the clots and low platelet counts.

“Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution,” Dr. Anne Schuchat, principal deputy director of the CDC, and Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a joint statement.

They are recommending that people who were given the J&J vaccine who are experiencing severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after receiving the shot contact their health care provider.

U.S. health authorities cautioned doctors against using a typical clot treatment, the blood-thinner heparin.

“In this setting, administration of heparin may be dangerous and alternative treatments need to be given,” the FDA and CDC said.

European authorities investigating the AstraZeneca cases have concluded clots appear to be similar to a very rare abnormal immune response that sometimes strikes people treated with heparin, leading to a temporary clotting disorder.

Officials say they also want to educate vaccine providers and health professionals about the “unique treatment” required for this type of clot.

Johnson & Johnson said it was aware of the reports of “thromboembolic events,” or blood clots, but that no link to its vaccine had been established.

“We are aware that thromboembolic events including those with thrombocytopenia have been reported with Covid-19 vaccines,” said Johnson & Johnson in a statement. “At present, no clear causal relationship has been established between these rare events and the Janssen Covid-19 vaccine.”

The J&J vaccine received emergency use authorization from the FDA in late February with great fanfare, with hopes that its single-dose and relatively simple storage requirements would speed vaccinations across the country. Yet the shot only makes up a small fraction of the doses administered in the U.S. as J&J has been plagued by production delays and manufacturing errors at the Baltimore plant of a contractor.

Last week the drugmaker took over the facility to scale up production in hopes of meeting its commitment to the U.S. government of providing about 100 million doses by the end of May.

Only about 9 million of the company’s doses have been delivered to states and are awaiting administration, according to CDC data.

[ Need a vaccine appointment? Channel 9′s Joe Bruno tracks open slots ]

Until now, concern about the unusual blood clots has centered on the vaccine from AstraZeneca, which has not yet received authorization in the U.S. Last week, European regulators said they found a possible link between the shots and a very rare type of blood clot that occurs together with low blood platelets, one that seems to occur more in younger people.

The European Medicines Agency stressed that the benefits of receiving the vaccine outweigh the risks for most people. But several countries have imposed limits on who can receive the vaccine; Britain recommended that people under 30 be offered alternatives.

But the J&J and AstraZeneca vaccines are made with the same technology. Leading COVID-19 vaccines train the body to recognize the spike protein that coats the outer surface of the coronavirus. But the J&J and AstraZeneca vaccines use a cold virus, called an adenovirus, to carry the spike gene into the body. J&J uses a human adenovirus to create its vaccine while AstraZeneca uses a chimpanzee version.

The announcement hit U.S. stock markets immediately, with Dow futures falling almost 200 points just over two hours before the opening bell. Shares of Johnson & Johnson dropped almost 3%.

NC, SC health leaders pausing administration of J&J vaccine

Shortly after the CDC and FDA announced they were investigating reports of potentially dangerous blood clots, the Carolinas said they would be pausing distribution of the J&J vaccine.

North Carolina said it would pause distribution “out of an abundance of caution” until there is more information available.

“Our primary concern is the health and safety of all North Carolinians. Out of an abundance of caution, we are following the recommendations of the FDA and CDC and have paused the administration of the Johnson & Johnson COVID-19 vaccine until we learn more. The safety system in place is working as it should. If you have an appointment for Pfizer or Moderna, please go to your appointment as planned. If you have an appointment for Johnson & Johnson, your appointment will be re-scheduled.”

NCDHHS Secretary Dr. Mandy Cohen confirmed none of the cases being investigated by the CDC and the FDA occurred in North Carolina.

Mecklenburg County announced it will also pause the use of Johnson & Johnson, as recommended by the FDA and the CDC.

“As public health officials, our primary concern is the health and safety of our residents,” Mecklenburg County Health Director Gibbie Harris said. “While we pause the use of the Johnson & Johnson vaccine, we still have two other safe and effective vaccines available in our community – Moderna and Pfizer. I encourage individuals to continue to seek out vaccination clinics offering those vaccines and make an appointment as soon as it is available to them.”

Harris said there were two Mecklenburg County vaccine events that were planned for Tuesday with the J&J vaccine and they switched to a different vaccine. The pause does not affect the county’s primary COVID-19 vaccination clinic at Bojangles Coliseum.

Harris stressed the importance of not letting what is happening with Johnson & Johnson discourage people from getting a COVID-19 vaccine.

“We continue to re-emphasize, there is no indication at this point in time that there’s any problem with the Pfizer and the Moderna vaccine,” Harris said. “There have been millions of doses provided and we have not seen anything like this with those.”

In South Carolina, health officials said they have alerted vaccine providers and are working with them to reschedule or change planned vaccine events that were going to use J&J.

“South Carolina public health officials received word this morning, like many throughout the nation and the state, that the CDC and FDA have recommended immediately pausing use of the Janssen vaccine due to concerns with blood clotting. Our top priority is protecting the health and safety of the public. This pause is evidence of very close safety monitoring as part of the strict quality assurance that is in place to ensure patient safety.

“DHEC has placed an immediate pause on our Janssen distribution and has contacted providers to alert them of this new development. In addition, we are currently in the process of rescheduling or changing planned vaccine types for events that were going to use Janssen.

“We recognize that this will impact our current supply of vaccines across the state and are awaiting to hear more information from the federal government. South Carolina, like most states, had been receiving a small amount of Janssen vaccine from the federal government — about 7,000 doses a week — compared to the more than 40,000 doses each of Pfizer and Moderna we receive each week. Because of this, the pause on Janssen vaccine is less of an impact in our state than we would experience if a pause occurred on Pfizer or Moderna vaccines. Millions of people in the United States have received doses of vaccines with very little side effects.

“We continue to encourage South Carolinians to get vaccinated against COVID-19 in order to best protect yourself and others and will keep everyone updated as we learn more about the Janssen vaccine.”

What should you do if you’ve already gotten the J&J vaccine?

Now that the FDA and the CDC have recommended a pause in the distribution of the Johnson & Johnson vaccine, many who have already received it may be wondering what they should do now.

The pause came after the agencies said they were investigating “unusual clots” in six women that happened six to 13 days after they received the vaccine.

[ J&J vaccine pause: What should you do if you’ve already gotten the vaccine ]

So what should you do if you had the Johnson & Johnson vaccine?

According to the CDC, if you have had severe headaches, abdominal pain, leg pain or shortness of breath three weeks after getting the vaccine, you should call your doctor.

If you have had no side effects that are associated with blood clots, health officials said the risk of having a reaction is unlikely.

Some North Carolina providers pausing J&J vaccinations

Some North Carolina vaccine providers are pausing Johnson & Johnson vaccinations after the CDC and the FDA announced they were investigating reports of potentially dangerous blood clots.

Walgreens told our news partner WTVD the chain will be pausing the use of J&J vaccine “immediately.” CVS also issued a statement after the announcement saying, “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.”

Locally, several pharmacies and vaccination clinics have paused the use of the J&J vaccine in the wake of the investigation. Some clinics have said they will still give vaccinations, but will switch to a different vaccine.

Moose Pharmacy was planning on having two vaccine clinics Tuesday using J&J, but the owner told Channel 9 he canceled both clinics after the FDA and the CDC’s decision to pause the vaccine.

[ Johnson & Johnson vaccine pause: What is cerebral venous sinus thrombosis? ]

Owner Joe Moose said the people who had scheduled those appointments were rescheduled for a Moderna vaccine slot in the near future.

“We’ve had to put the brakes on and stop J&J product,” Moose said. “We still have the other manufacturer’s products. We have other shots you can choose and we’re trying to get people rescheduled with those.”

Moose said his phone rang non-stop Tuesday. He said many people want to know how serious the blood clot problem is and who is most likely to be impacted by it.

Moose said J&J product has been increasing, and the pharmacy had about 500 appointments scheduled for this week with even more product slated to arrive Tuesday.

[ REGISTER NOW: WSOC-TV and community partners come together in race to vaccinate ]

Channel 9 is partnering with the Mecklenburg County Health Department for a vaccine clinic Saturday. The health department will switch from the J&J vaccine to Pfizer. The clinic will run from 9 a.m. to 4 p.m. at Camp North End.

Both Novant and Atrium said they were also pausing J&J vaccinations while the CDC and the FDA conduct their investigations.

(Watch the video below as Channel 9′s Dave Faherty explains how the Burke County Health Department had to switch from J&J to Moderna in order to administer vaccines to those who are homebound)

What will colleges using the J&J vaccine do?

Johnson & Johnson vaccinations are now paused across the Carolinas and across the country. Colleges have been turning to the vaccine because it is one-dose and there is no need for a follow-up shot so close to graduation and the end of the semester.

Across the Charlotte area, the University of North Carolina at Charlotte said 2,400 students, faculty and staff have received the J&J vaccine and the most recent clinic was held on Monday.

Freshman Melissa Zelenik was one of the students who rolled up her sleeve for the vaccine.

“It was so convenient and it was one less thing to worry about,” Zelenik said. “It helps keep other people safe.”

Now, UNCC said they won’t be using J&J until the FDA and the CDC finish their investigation.

Last month, 6,000 people got the vaccine at Johnson C. Smith University and 400 members of the Johnson and Wales campus community received the J&J shot.

Appalachian State University told Channel 9′s Dave Faherty that 3,800 students and staff have received the J&J vaccine so far but at their next clinic on Thursday, they will be giving out Moderna shots instead.

NC has 85,000 other vaccines for those with J&J appointments

By BRYAN ANDERSON/AP

North Carolina has 85,000 doses of the Pfizer and Moderna vaccines it will offer to people who had been scheduled to receive a single-dose Johnson & Johnson COVID-19 vaccine starting Tuesday, state health officials said in an afternoon news conference.

In response to federal guidance it received Tuesday morning to stop administering J&J doses over concerns of six rare cases of serious blood clots, the state Department of Health and Human Services swiftly told providers to offer a different vaccine or reschedule appointments to prospective J&J recipients.

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Less than 7% of the nearly 3.7 million people at least partially vaccinated in North Carolina have gotten a Johnson & Johnson vaccine. Experts and health officials don’t want Tuesday’s development to discourage already reluctant people from getting the vaccine.

If anything, they say the public should have more confidence in the system, particularly with the Pfizer and Moderna vaccines, which have not seen similar issues as J&J and have been administered since December 2020 -- more than two months before Johnson & Johnson’s vaccine received approval from U.S. regulators.

“The safety system in place is working as it should,” said Mandy Cohen, North Carolina’s top public health official. “These adverse events appear to be extremely rare.”

The six severe blood clotting cases represent a microscopic share of the more than 7.1 million people who have gotten a J&J vaccine nationwide, according to the latest CDC data.

North Carolina’s 85,000 Pfizer and Moderna replacement doses will draw mostly from existing supply that went unused last week.

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Cohen urged people who received a J&J vaccine in the past three weeks to contact their health care provider if they experienced severe headaches, abdominal pain, leg pain or shortness of breath three days after they were inoculated. Temporary reactions and minor symptoms, such as achiness, are common shortly after vaccination and a sign the shot is working as it should.

Cameron Wolfe, an infectious disease expert with Duke Health, told reporters Tuesday that he is happy to pivot to Moderna and Pfizer vaccines as the federal government reviews the clotting cases associated with the J&J vaccine, but called the single-dose shots “a valuable part of our arsenal” because of their ability to be more easily stored and administered to people less likely to return for a second shot.

The Associated Press and The Cox Media Group National Content Desk contributed to this report.