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By Gary Evans, Medical Writer
Public health officials in the United States have recommended a cautionary pause to administering the Johnson & Johnson/Janssen (J&J/Janssen) COVID-19 vaccine because of what appears to be a very rare immune reaction that causes severe blood clots. The reaction has not been observed in the other two vaccines approved for use in the United States, and they can continue to be administered.
At an April 13, 2021 press conference, the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) reported that there have been six blood clot cases in the United States after more than 6.8 million doses of the one-shot J&J/Janssen vaccine were administered.
All six cases occurred among women between the ages of 18 and 48 years of age, with symptoms occurring from six to 13 days after vaccination.
“Initial presenting symptoms were notable for headache in five of six patients, and back pain in the sixth who subsequently developed a headache,” a CDC health alert issued the same day noted. “One patient also had abdominal pain, nausea, and vomiting. Four developed focal neurological symptoms (focal weakness, aphasia, visual disturbance) prompting presentation for emergency care. The median days from vaccination to hospital admission was 15 days (range = 10-17 days). … Four patients developed intraparenchymal brain hemorrhage and one subsequently died.”
A key reason for the vaccination pause is to alert providers that normal anticoagulation treatment for blood clots like heparin may make this rare reaction worse. Providers should ask about a history of recent immunization with the Janssen vaccine if people present with severe headache, abdominal pain, leg pain, or shortness of breath.
“The issue here with these type of blood clots is that if one administers the standard treatments, one can actually cause tremendous harm or the outcome can be fatal,” said Peter Marks, MD, PhD, director of the Center for Biologics Evaluation and Research at the FDA. “We want to make sure if providers see people with low blood platelets or if they see people who have blood clots, they need to inquire about the history of recent vaccination.”
In the six cases, cerebral venous sinus thrombosis (CVST) was seen in combination with thrombocytopenia — low levels of blood platelets. It is the combination of CVST clots and low platelet counts that is unusual and needs to be better understood to begin vaccinating again, he said.
“The combination here — the real thing that is so notable — is not cerebral venous sinus thrombosis or thrombocytopenia,” he said. “Those two things can occur. It is the occurrence together that makes a pattern, and that pattern is very similar to what was seen in Europe with [AstraZeneca vaccine].”
The current theory is that the reaction is a very rare immune response “that leads to activation of platelets,” Marks said.
Both the Janssen and AstraZeneca vaccines use benign adenoviruses to spur an immune reaction to SARS-CoV-2 spike proteins and prevent infection. The FDA will look for such rare adverse reactions in other adenovirus vaccines, Marks said. Although the FDA has the regulatory power to take stronger action, the pause is not a “mandate” and individual providers and patients can weigh the currently known risk of this side effect against the risk of acquiring COVID-19.
The CDC will convene an emergency meeting of its Advisory Committee on Immunization Practices (ACIP) on Wednesday, April 14 to further review the six cases.
“I know there are people who have gotten the vaccine are probably very concerned,” said Anne Schuchat, MD, principal deputy director of the CDC. “For people who got the vaccine more than a month ago, the risk is very low at this time. For people who recently got the vaccine in the last couple of days, they should be aware and look for any [of the] symptoms.”
The CDC alert included the following recommendations for clinicians: