FDA and CDC officials recommended pausing administration of the Johnson & Johnson COVID vaccine “out of an abundance of caution,” and mainly for the benefit of clinicians to respond to associated serious events.
This comes after six cases of cerebral venous sinus thrombosis (CVST) combined with thrombocytopenia were reported in the US, all among women ages 18-48. With approximately 6.8 million doses administered in the U.S., it suggests a one-in-a-million risk.
J&J has halted distribution of its vaccine in Europe, reportedly taking officials there by surprise. South Africa has also paused the vaccine rollout.
At a media briefing, when asked whether pausing administration of the vaccine was an “overreaction,” Acting FDA Commissioner Janet Woodcock, MD, said the aim was to provide “time for the healthcare community to learn what they needed about how to diagnose, treat, and report” such events.
FDA’s director for the Center for Biologics Evaluation and Research, Peter Marks, MD, PhD, noted that the condition involves a rare blood clot for which heparin or related anticoagulants is not the standard treatment.
“The issue with these types of blood clots is if one administered standard treatment, one can actually cause tremendous harm or the outcome can be fatal,” he said. “One needs to make sure providers are aware if they see people with low blood platelets or blood clots, to inquire about recent vaccination and act accordingly.”
The background rate of CVST is 2-14 per million in the setting of a normal platelet count, but thrombocytopenia together with abnormal clotting makes it a “pattern.” CVST symptoms also include severe headache, abdominal pain, leg pain, and shortness of breath.
Marks noted that vaccination-related headaches tend to resolve within a few days, whereas CVST symptoms could manifest over a week post-vaccination, and closer to a patient presenting to the emergency department with severe headache. No such rare events have been seen more than 3 weeks post-vaccination.
Dr Marks also said that this pause is a recommendation but does not prevent healthcare providers from providing the J&J vaccine to their patients should benefits of vaccination outweigh the risks.
“We’re not going to stop a provider from administering a vaccine,” he added. “The benefit/risk will be beneficial overall to that individual in a large majority of cases.”
Dr Marks said that while they don’t have a “definitive cause” for the adverse reactions, data from AstraZeneca on similar events in Europe, it is likely a “similar mechanism” with the J&J vaccine. An autoantibody against platelet factor 4 has recently been identified as the trigger for the reaction.
“The immune response occurs rarely after some people receive the vaccine, and that immune response leads to the activation of platelets and extremely rare blood clots,” he said.
However, Marks stopped short of calling it a “class effect,” meaning it was related to the viral vector vaccine itself. He said he wasn’t ready to make a “broad statement yet,” but “obviously it’s from the same general class of viral vectors.”
The AstraZeneca, J&J and Sputnik V vaccines all use adenovirus vectors to deliver antigens. The rate CVST for AstraZeneca was estimated by European officials to be about 5 per million doses. Though Sputnik V has no confirmed CVST cases, a recent report suggests a possibility.
Besides these, the Ebola vaccines are the only other ones to use adenovirus vectors.
Woodcock said that all US cases were in women of reproductive age, with one death and one hospitalisation, but Marks said it was not clear there was any association with hormonal contraception, which also carries a small thrombosis risk. The cases did not have any preexisting conditions which could have explained the events.
The American College of Obstetricians and Gynecologists (ACOG) noted there is no “clear phenotype” for women who may experience this complication.
“Until there is a better understanding of the frequency and impact of this finding, it will be important to encourage pregnant and postpartum women who wish to be vaccinated to receive the mRNA vaccines: Pfizer or Moderna,” said Christopher Zahn, MD, vice president for practice activities at ACOG, in a statement.
“If venous thrombosis is noted in the setting of thrombocytopenia, treatment includes intravenous immunoglobulin and other supportive care,” Dr Zahn added.
Source: MedPage Today
