With Johnson & Johnson’s COVID-19 vaccine still on hold in the United States after reports of a rare but serious blood clotting disorder in a small number of the approximately 7 million people who have received the vaccine, experts in health they now focus on what might be behind these rare adverse events.
Doctors, scientists and public health experts are heading to Europe for clues, where a similar vaccine made by AstraZeneca – not yet authorized in the US – has also been linked to several rare blood clots.
“AstraZeneca and Johnson & Johnson vaccines are manufactured similarly,” said Dr. William Schaffner, an infectious disease physician at Vanderbilt University with experience in preventive medicine and health policies. “But carriers are different types of adenovirus … that’s part of the general information, why there’s a pause now.”
“It’s hard to say if it’s the same problem,” said Dr. Richard Kuhn, a doctor of medicine, a virology expert at Purdue University, “but the vaccine appears to cause an antibody response that activates platelets, which causes clots “.
While many experts have been hesitant to say for sure if there is a link, Schaffner said there is a growing consensus in the scientific community after none of these rare clots have been linked to Pfizer or Moderna vaccines, which they use mRNA, a different technology.
“I don’t think we should be upset about that,” Schaffner said, adding that it may be time to “accept the fact that these are vaccine-induced events, but very rare.”
But experts warned that even if there is a link, current evidence suggests that the risk of developing a blood clot after receiving the Johnson & Johnson vaccine is extremely low – in fact, lower than a lightning bolt.
In response to a report on one of six cases of clots published in the New England Journal of Medicine, Johnson & Johnson responded Friday, insisting that a clear link has not yet been established.
“At this time, the evidence is not sufficient to establish a causal relationship between these events and the [Johnson & Johnson] Janssen’s scientists added that the vectors used in his vaccine and AstraZeneca are “substantially different” and that these differences could lead to “quite different biological effects.” due to this coagulation, combined with a low platelet count in those receiving the COVID-19 vaccine.
Next week, the Independent Advisory Committee of the Centers for Disease Control and Prevention will review all tests and make a recommendation on whether to continue using J&J vaccines.
Different theories
Even with more questions than answers, scientists are exploring different theories about why such traits (called viral vector vaccines) can cause rare clotting problems.
Vaccines work by inciting our immune systems to develop antibodies against a virus, and the dominant theory is that viral vector vaccines somehow trigger an abnormal immune response that leads to blood clots.
Scientists in Germany identified a specific antibody in many people who developed clots after receiving the AstraZeneca vaccine, and later U.S. researchers identified the same antibody in individuals who developed similar clots after receiving a J&J vaccine. In these subjects, the body’s immune system has formed antibodies that bind to platelets, the specialized blood cells that bind together to form clots.
“It’s not the vaccine that causes it, it’s the body’s immune response to the vaccine,” said Dr. Alex Spyropoulos, a blood clot specialist and professor at Feinstein’s Medical Research Institutes.
Experts say the disease, cerebral venous thrombosis or CVST, is extremely rare.
The Food and Drug Administration and the CDC said that in the six women who experienced a clot, the problem manifested itself six to 13 days after receiving the vaccine, a period of time that continues with an immune response. dir Spyropoulos.
It is not yet clear why a vaccine would cause this cascade of events, but researchers said it mimics another well-documented reaction to heparin, a blood anticoagulant. For this reason, the CDC and the FDA have warned against the use of heparin to treat anyone recently vaccinated with the Johnson & Johnson vaccine.
Existing evidence from the United States and Europe suggests that women may be at higher risk, perhaps in part because women are already more likely than men to develop CVST, according to previous data.
“We need to be careful about the assumptions we make,” Spryopoulos warned, “especially considering how often these events have occurred.”
Similar cases may develop in men, but if the CDC advisory group concludes that the risk is higher in women, the FDA could move toward a black box warning (a label for drugs and medical devices with effects potentially serious side effects) in the Johnson & Johnson Vaccine for certain women.
While the abrupt cessation of an already authorized vaccine may instill concerns and encourage hesitation around the vaccine, experts said it is a good sign that the drugs are being properly controlled for safety.
“I really want to emphasize to the public that they need to stay confident in our concepts and times related to vaccines in general,” Dr. that the general public “do not allow this to be sour your decision to vaccinate yourself in general.”
“We have confidence in the process,” Goldman added. “And we will make the right decision on public safety.”
Amanda Benarroch, MD, a psychiatric resident at the Mayo Clinic in Rochester, Minnesota, is a contributor to the ABC News Medical Unit. Sasha Pezenik and Sony Salzman of ABC News contributed to this report.