“The CDC and the FDA are taking these concerns about blood clots and the J&J vaccine seriously and are diligently assembling data,” the official said.
An expert outside the government who is familiar with the situation agreed that health officials are taking the matter seriously.
“The CDC is very concerned and they’re very working hard on this and monitoring this closely,” said the expert, who spoke on the condition of anonymity due to the sensitive nature of the issue.
The concern in the United States isn’t just about the Johnson & Johnson shot per se. At a time when US health officials are encouraging Americans to get vaccinated as soon as they can, there’s a worry that news coverage about clots being studied in relation to Johnson & Johnson’s vaccine might make some Americans more hesitant to get any Covid-19 vaccine.
Vaccine hesitancy is already an issue in the US, and officials at the US Centers for Disease Control and Prevention and the US Food and Drug Administration are “thinking through how to communicate about the issue without creating the impression that something might be wrong with the [Johnson & Johnson] vaccine,” the federal health official said.
Another expert familiar with the situation said that was the right approach, stressing the importance of communicating without scaring people.
“I would hope that HHS is having a confab about this right now,” the expert said, referring to the US Department of Health and Human Services.
In a statement, Johnson & Johnson said its tracking of side effects revealed “a small number of very rare events following vaccination. At present, no clear causal relationship has been established between these rare events and the [Johnson & Johson] COVID-19 vaccine.”
The FDA released a statement last week that it was aware of reports of “serious thromboembolic events” in the US that occurred “in a few individuals following receipt of the [Johnson & Johnson] COVID-19 vaccines” and that “at this time we have not found a causal relationship with vaccination.”
J&J study participant’s illness revealed
What made FDA scientists take note, however, is that in the trial, about the same number of people received a placebo — a shot of saline that does nothing — as received the vaccine. However, when comparing the two groups, more study participants developed clots after receiving the vaccine than the placebo.
Calling it a “slight numerical imbalance,” the FDA noted that there were 15 events in 14 participants who received the vaccine, compared to 10 events in 10 participants who received the placebo.
The FDA report concluded that given this imbalance, “vaccine cannot be excluded as a contributing factor,” and that the FDA would recommend “surveillance” for blood clots once the vaccine was rolled out.
In this context, Andy Slavitt, White House senior adviser for Covid-19, said at a news briefing on Monday that the United States is still on track to reach its Covid-19 vaccination targets even without additional doses from Johnson & Johnson.
Scrutiny over blood clots
This isn’t the first time blood clots have come up in relation to a Covid-19 vaccine.
The AstraZeneca vaccine, which has not been authorized in the United States, has been authorized in more than 70 countries. The J&J vaccine and the AstraZeneca vaccines are similar — they both use adenovirus vectors to make them work.
By March, doctors in several European countries had begun to notice “very rare” cases of unusual blood clots among people who received the AstraZeneca vaccine.
The agency noted that its safety committee reviewed 62 cases of cerebral venous sinus thrombosis and 24 cases of splanchnic vein thrombosis, a type of blood clot in the abdomen, 18 of which were fatal. The cases were reported at a time when 25 million people in Europe and the UK had received the vaccine.
The European agency concluded that unusual blood clots with low blood platelets should be listed as “very rare side effects” of the AstraZeneca vaccine. While advising the public to look out for the signs of clots, the regulators said the benefits of the shot were still worth the risk.
The European Union authorized J&J’s vaccine last month, and it’s expected to be rolled out there in the next few weeks.
A ‘vaccine-induced’ condition
Hematologists say this isn’t the first time they’ve seen unusual blood clots with low platelet levels. Sometimes people who are given a very common blood thinner called heparin can develop the condition.
But the people who received the AstraZeneca vaccine and developed the clots hadn’t taken heparin.
“It’s actually very interesting,” said Dr. Peter Kouides, immediate past president of the Thrombosis and Hemostasis Societies of North America. “The risk is very, very low, but it does seem to be a true disorder triggered by the vaccine.”
He said there are treatments for this “very serious condition,” but they don’t always work.
“When you have [this] happen, all bets are off,” said Dr. Hanny Al-Samkari, a hematologist and instructor at Harvard Medical School. “You can get clots anywhere. You can get them in your brain, in your belly, in your extremities, in your heart — it doesn’t matter. They can happen just about anywhere and obviously that’s often problematic and/or fatal.”
Harsh words for Johnson & Johnson
One part of J&J’s statement drew ire from a prominent vaccine adviser to the FDA, as it seemed to say there were similar safety concerns about Pfizer and Moderna’s vaccines, too — which, he said, simply is not true.
“We are aware that thromboembolic events including those with thrombocytopenia have been reported with all COVID-19 vaccine,” according to the Johnson & Johnson statement.
Considering that’s such a large number, it’s not surprising some in this group would experience thrombocytopenia, a condition where there are low levels of platelets in the blood, said Dr. Paul Offit, a member of the FDA’s Vaccines and Related Biological Products Advisory Committee. The issue, he said, is whether that number of people exceeded what would be expected if they had not been vaccinated.
“That is a really irresponsible thing to say,” Offit said, referring to the J&J statement. “It will unnecessarily scare people about Moderna and Pfizer when not only is there no evidence it’s a problem — there’s evidence there is not a problem,” added Offit.
A J&J spokesman declined to comment on Offit’s criticism.
CNN’s Lauren Mascarenhas, Michelle Watson and Jacqueline Howard contributed to this report.