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Clinicians should pay close attention to patients with suspected thrombotic events or thrombocytopenia following vaccination with the Johnson & Johnson COVID-19 vaccine, including consulting a hematologist, CDC staff said on a call with clinicians on Thursday.

A cautioned that clinicians should have a "high index of suspicion" for patients with these events. Following a vaccination history, they should be evaluated with a screening platelet factor 4 (PF4) enzyme-linked assay, such as what would be performed for autoimmune heparin-induced thrombocytopenia (HIT). Moreover, these patients should not be treated with heparin unless HIT testing is negative.

CDC staff held this call to inform clinicians about the "pause" in Johnson & Johnson's COVID-19 vaccine due to six cases of cerebral venous sinus thrombosis (CVST) with thrombocytopenia following vaccination, including one fatal case, first announced by CDC and FDA on Tuesday. CDC's Advisory Committee on Immunization Practices (ACIP) agreed to extend this pause until more information on the cases is available.

On this call, Tom Shimabukuro, MD, of the CDC, reminded clinicians to report all serious adverse events to the HHS Vaccine Adverse Events Reporting System (VAERS), adding that they may then be contacted by VAERS or CDC to release patient medical records.

"HIPAA permits reporting of protected health information to public health authorities, including CDC and FDA," he said. "There are no HIPAA issues with providing this information to CDC, and we appreciate your cooperation."

CDC staff also told clinicians to consult with a hematologist for these patients, and Sara Oliver, MD, of the CDC, even recommended that "a screening CBC [complete blood count] might be informative" to detect these rare events.

However, a CBC should only be in the setting of a recently vaccinated patient who presents with concerning symptoms, and she recommended against patients taking prophylactic aspirin, for example.

"Ultimately, we're not saying everyone with [Johnson & Johnson] vaccine needs to start getting serial CBCs," Oliver said, adding that if a clinician has certain concerns about anticoagulation for any patient, they should consult a hematologist.

She also said a hematologist should be consulted when clinicians asked about whether or not to give heparin to vaccinated dialysis patients, as well as in response to questions about treatment for oncology patients on drugs that normally decrease platelet counts.

Clinicians inquired if headaches related to CVST were "aneurysm-like," but Shimabukuro said that the "initial presentation was not particularly notable" enough to stand out, though he did not have "specifics of the narratives given."

Oliver presented data showing that the vaccine was available as of March 2, and prior to March 30, 48% of total doses were administered. However, 52% of doses were administered from March 31 to April 13, and thrombocytopenic thrombotic events may still occur, as symptoms tend to show up 1-2 weeks following vaccination. Indeed, the first case of CVST with thrombocytopenia occurred on March 19, with cases through April 12.

She added that while these events appear similar to those occurring following AstraZeneca's COVID-19 vaccine in Europe, they are "still learning the extent to which those cases represent the same syndrome."

Shimabukuro was asked why this complication didn't occur following administration of other adenoviral vector vaccines, such as the Ebola vaccine. Because Ebola vaccine use was on the order of "hundreds of thousands," not millions or tens of millions, rare adverse events would be less likely to be detected, he said.

Oliver said ACIP will reconvene in 1 to 2 weeks to discuss additional accumulated data, and hopefully make more formal recommendations on vaccine use.

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