National Guardsmen direct motorists where to go to receive the COVID-19 vaccine after their information is verified at the Neshoba County Coliseum in Philadelphia. Credit: Vickie D. King/Mississippi Today

COVID-19 vaccination efforts in the United States were slowed by an unexpected hurdle on Tuesday after federal health agencies recommended a pause in the use of Johnson & Johnson’s single-dose coronavirus vaccine after six recipients developed an extremely rare blood clot.

“We are recommending a pause in the use of this vaccine out of an abundance of caution,” Dr. Peter Marks, director of the Food and Drug Administration’s Center for Biologics Evaluation and Research, and Dr. Anne Schuchat, principal deputy director of the U.S. Centers for Disease Control and Prevention, said in a joint statement. “Right now, these adverse events appear to be extremely rare.”

Health officials have said that the pause is only expected to last a few days. In response, state health departments across the country, including in Mississippi, have either instructed or advised health providers to halt the use of the vaccine while the blood clotting issue is investigated. The pharmacy giants CVS and Walgreens have also said that they will stop administering the Johnson & Johnson vaccine and will reschedule the appointments of affected patients as soon as possible.

Mississippi State Health Officer Dr. Thomas Dobbs tweeted Tuesday morning that the Mississippi State Department of Health is instructing vaccine providers in the state to refrain from using the Johnson & Johnson vaccine until more guidance is available from federal health agencies. 

Dobbs also told the nearly 42,000 Mississippians who have received the Johnson & Johnson vaccine not to worry, noting that the window of risk for developing the rare blood clot after receiving the vaccine appears short, and the likelihood of it happening at all is very slim.

During a press briefing on Tuesday, State Epidemiologist, Dr. Paul Byers, said that MSDH will work with vaccine providers that have received Johnson & Johnson shipments to replace those doses with Pfizer or Moderna doses if needed.

All six patients known to have developed the rare blood clot, known as cerebral venous sinus thrombosis, were women between the ages of 18 and 48 and developed the clotting within two weeks of vaccination. One of the six has died from the illness, and another has been hospitalized in critical condition. 

The CDC will hold a meeting of its Advisory Committee on Immunization Practices (ACIP) on Wednesday to further review these cases and assess whether they were caused by an immune system response triggered by the vaccine. The FDA will review these findings alongside their own investigation to determine the future status of the vaccine’s Emergency Use Authorization. 

Treating the type of blood clot observed in these cases is another area of concern, as it might be dangerous to administer the drug commonly used to treat blood clots. Dobbs said that the federal review of this issue was 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.”

Nearly seven million people in the U.S. have received the Johnson & Johnson vaccine, according to CDC data. This represents only a tiny fraction of the more than 187 million doses of COVID-19 vaccines that have been administered across the country.

MAP: Where Mississippians can get the COVID-19 vaccine 

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Will Stribling covered healthcare and breaking news for Mississippi Today.