Medical experts on Thursday’s Grand Rounds delved into the risks posed by the Johnson & Johnson vaccine, which the United States stopped distributing last week after reports of rare and dangerous blood clots in six recipients.
The clots were documented in women between the ages of 18 and 48, about a one-in-a-million occurrence, as about 7 million J&J doses have been administered so far in the United States.
“When you say rare and serious [to the public], they focus on ‘serious’ and tune out ‘rare’ — and that’s human nature,” said Dr. John Moore, a virology and immunology expert from Cornell University. “It was always likely that something unfortunate could have happened when you’re vaccinating hundreds of millions and ultimately billions of people.”
Similar blood clotting issues have cropped up with the AstraZeneca vaccine which, with the J&J shot, China’s CanSino and Russia’s Sputnik V, is part of a family of vaccines created using adenoviruses, which are a group of common viruses, including colds, sore throats and pinkeye.
No such reports have surfaced for the Moderna and Pfizer vaccines, which are both based on mRNA technology.
“It’s a reasonable assumption that it’s specific to the adenovirus vectors,” Moore said, describing the adenovirus vaccines as “variations on the same theme.” Russia and China have staunchly denied that their vaccines could cause blood clots.
“Of course if they saw something like this with the Sputnik V, program they probably wouldn’t be shouting it from the rooftops,” Moore said.
Federal health agencies will likely decide whether to recommend resuming administering the J&J shot by Friday, the experts said. This could include recommending the vaccine come with with warnings attached or that it be used only in certain populations, like men and women older than childbearing age.
J&J delayed its rollout in Europe after U.S. regulators recommended a pause in its domestic distribution, but the region’s health regulator said the benefits of the shot outweighed the risk of blood clots, and on Tuesday, officials there said the European Union it will resume rolling out the vaccine.
Moore said the CDC didn’t have a choice in pausing J&J, especially given media reports of serious adverse effects and at least one death. If the vaccine is resumed or resumed even in subpopulations, public confidence could even be boosted by the government’s quick response, he added.
“They had to act,” he said. “Whether they got the reaction perfect, different people see it in different ways. It’s easy to be a Monday morning quarterback on something like this.”
He also said that the blood clots are not an indication that the vaccines are generally unsafe or were not properly vetted. Such side effects are incredibly rare, and clinical trials with 20,000 or 30,000 patient volunteers are unlikely to pick up on incidents that occur at a one-in-a-million rate.
Moderator Dr. Bob Wachter, chair of UCSF’s medicine department, added that blood clotting is an unusual side effect to see in a vaccine.
Later in the talk, Dr. Andrew Leavitt, a UCSF hematology expert, broke down the potential mechanisms by which the J&J vaccine could cause blood clotting.
Symptoms of blood clotting appear to show up between 5 and 28 days after vaccination, and can present in a variety of ways, including severe headache, shortness of breath, and new bruising, Leavitt said.
The closest comparison to the blood clotting phenomenon seen with the vaccinations is the clotting that occurs in patients with blood clotting caused by “spontaneous” heparin-induced thrombocytopenia (HIT), Leavitt said.
Although there is no heparin in the vaccines, knowing this is important, as in these cases, treating the problem with heparin would make it worse. And getting this information out to doctors treating patients after a J&J shot could save lives, Leavitt said.
“The pause has been incredibly valuable in letting enough clinicians understand this and be on the lookout,” he said.
“I wouldn’t be surprised, but I’ll never be able to prove it, but this pause could help folks who’ve had the vaccine and are now going through their 24 day period, and maybe they will get treated more appropriately sooner, and will have better outcomes,” he added.