What we know about clotting with the Johnson & Johnson vaccine — and why the U.S. was right to hit pause

Researchers need to find answers, and consumers need to weigh the various risks even as the CDC allows those vaccinations to resume.

(Mary Altaffer | AP) The Johnson & Johnson COVID-19 vaccine sits on a table at a pop up vaccinations site the Albanian Islamic Cultural Center, in the Staten Island borough of New York, Thursday, April 8, 2021. The U.S “paused” administration of the single-dose Johnson & Johnson COVID-19 vaccine to investigate reports of potentially dangerous blood clots.

The Johnson & Johnson vaccine clotting issue is fascinating. It’s also, if we’re completely honest about it, a bit frightening.

To catch you up: The Food and Drug Administration and the Centers for Disease Control and Prevention announced last week that they had discovered a number of cases of blood-clotting problems as a result of the J&J vaccine, and put a temporary pause on injecting more people with it.

This week, the European Union’s regulatory agency looked at that same number of cases and said that, yes, there should be a warning in the product information about these clots, but, ultimately, the benefits of the vaccine outweigh the detriments.

On Friday, the CDC’s Advisory Committee on Immunization Practices met to discuss the matter. In the end, the agency cleared the way for the vaccine’s use to resume — with a warning label that explained the risk of clotting issues.

Naturally, the pause gave people, well, pause — and spurred a lot of questions. What’s causing these clots? How likely are they to happen? Who gets them, and why? How dangerous is this vaccine compared to the risk of COVID-19?

Here’s what you need to know:

What’s going on here?

Small numbers of recipients of the J&J and the overseas-approved AstraZeneca vaccines have developed blood clotting. In the U.S., we know of eight cases in relation to the J&J shot. One person died, three recovered, and four remain hospitalized.

The most worrying of these blood clots is called CVST, or cerebral venous sinus thrombosis. That’s when the veins taking blood out of your brain are blocked, leading to headaches at first, then stronger reactions, like stroke, later. It’s legitimately dangerous.

Of those eight cases, seven were women — ages 18, 25, 26, 28, 38, 45 and 48. It’s still a small number, but it appears to be happening more often in younger adults and in females.

Why in the world are these particular vaccines causing these clots? Scientists are still trying to figure that out, but they have a few good pieces of information with which to work.

First, people with this clotting problem have been found to have low platelet counts — platelets are the cells in your bloodstream that generally cause good clotting to occur, like when you get a cut and the bleeding eventually stops.

Second, they’ve also seen that there are elevated levels of antibodies to platelet factor 4 in these people — levels that are also sometimes but rarely seen when people are given heparin, a drug given to heart attack patients and the like to prevent clotting from happening. Those people also can have clotting problems.

Third, they’ve found that these clotting issues are not happening with the mRNA vaccines, Pfizer and Moderna. But they are happening — again, rarely — with the vaccines (J&J and AstraZeneca) that use an adapted adenovirus (a version of the common cold) to teach the body about the coronavirus’s spike protein.

So why would that adenovirus lead, in some people, to increased production of those antibodies to platelet factor 4, just like heparin does? We don’t know. Maybe they have similar shapes or chemical components? Would people who get the common cold via the adenovirus also get these clots? Those are the next steps of research.

What’s the actual risk of all of this?

Now I know what you’re thinking: We know of only eight cases out of about 7 million people who have received the J&J vaccine. And only one death. People have higher risks of dying all the time — from driving, cheerleading, taking all sorts of various medicines, and, of course, from COVID-19 itself.

But because J&J’s vaccine is so new, it’s also worth looking at other sources of data. In particular, going to the AstraZeneca’s vaccine dataset internationally might give us a more exact idea of what’s going on with the adenovirus vaccines. In the United Kingdom, researchers have found about five of these cases of severe clotting per million of people vaccinated.

How does that compare with the risk from COVID-19? Well, first of all, it depends on how old you are. Because it appears these clots are driven by an immune system overreaction, we’re actually seeing more clotting in younger adults than older ones. On the other hand, and as you know, COVID-19 is a lot more dangerous for older adults than younger ones.

It also depends, obviously, on how likely you are to catch COVID-19 in your community. If there’s a lot of spread, coronavirus is a more pressing threat.

So the British government made graphs to compare the risk of going to the intensive care unit for COVID-19 with the risk of having serious harms from the vaccine, at various levels of spread. This one is for about two cases per 10,000 people per day — roughly what the U.K. faced in March and also roughly what we’re facing in Utah in April.

Comparing the risk of COVID-19 vs the risk of blood clotting due to the vaccine, according to data from the U.K. (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/976877/CovidStats_07-04-21-final.pdf)

You can see what the result is: For everyone 40 or over, it’s probably better to get an adenovirus vaccine than nothing at all. For those under? Well, it’s a much closer call.

For those making a decision in the U.S. and Utah, we have an advantage: We have this whole class of vaccines from Pfizer and Moderna that don’t have these issues. While supply of those vaccines has been limited, that’s becoming less and less of a problem. For example, any Utahns over 16 can get vaccinated in Utah County today if they so choose. For many, especially young adults, it may make sense to prioritize one of those other vaccines, even if it means two doses instead of one, or an extra wait to get vaccinated.

The FDA’s decision and noble lies

The announcement to pause J&J vaccine injections garnered applause and criticism. Everyone understands being careful with vaccine safety, but there’s a real worry: Will huge publication of rare vaccine safety issues cause more people not to get vaccinated? If this causes fewer people to get vaccinated overall, it will likely cause more risk to life than the blood clotting problems do.

Overall, according to an Ipsos poll, 91% of Americans were aware of the pause in the J&J vaccine — an impressive number! Furthermore, 88% of those people said that the FDA and CDC were acting responsibly in pausing the vaccine, including a nearly equal split of Republicans and Democrats.

But, most importantly, it doesn’t look like the percentage of poll respondents who say they’re not likely to get the vaccine is changing, with 20% saying they’re not likely to get the vaccine — just about the same number as in January. In fact, that number has stayed consistent for months. Meanwhile, the number of people getting vaccinated continues to rise.

Most Americans are aware of and support the pause in the Johnson and Johnson vaccine. Furthermore, the rates of vaccine hesitancy don't seem to have changed after the news. (https://www.ipsos.com/en-us/news-polls/axios-ipsos-coronavirus-index)

I truly understand the concern here, and we’ll see how it plays out in reality. Polls aren’t vaccinations. But if the surveys are accurate, the biggest impact of the pause may be delayed vaccinations for a few million Americans for a couple of weeks. That’s not nothing, but delayed vaccinations are a lot better than canceled ones.

In general, I think the FDA leaning toward transparency and caution is the right move here. Sometimes, we’re too eager to make the “noble lie,” the kind of simplifications that result in more people doing the right thing but at the cost of telling the full truth about what’s going on.

But noble lies can have consequences. I think one cause behind some of the mask battles was experts’ early proclamations that the everyday public didn’t need to wear masks. They said this to protect the protective supply for health care officials. It was a noble goal, but the lie resulted in significant distrust later of those experts.

We’re going to be better off with greater trust between the public and medical officials, both for this pandemic and the next public health crisis to emerge, whatever it is. It’s important to champion the vast and impressive successes of the vaccination program, but to acknowledge the not-so-perfect elements, too.

Andy Larsen is a data columnist. He is also one of The Salt Lake Tribune’s Utah Jazz beat writers. You can reach him at alarsen@sltrib.com.