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Federal authorities on Tuesday recommended that states stop using Johnson & Johnson’s Covid-19 vaccine while an investigation is conducted into six serious cases of clotting problems — one of which was fatal — that were reported among women who received the vaccine.

The blood clots are similar to those reported by several European countries after use of AstraZeneca’s Covid-19 vaccine. And they are similar to an event that occurred during Johnson & Johnson’s U.S.-based clinical trial, an event that led to a temporary pause in that trial last fall. That case involved a man in his 20s, STAT reported at the time.


The clotting problem appears to be quite rare. As of Monday, more than 6.8 million doses of the Johnson & Johnson vaccine had been administered in this country. But officials acknowledged the investigation — and increased use of the vaccine, which was shipped in record numbers last week — could lead to the discovery of more cases.

The concern over Johnson & Johnson’s vaccine is raising questions about whether there is what’s known as a “class effect” — a problem one would expect to see with all vaccines made in the way the J&J and AstraZeneca vaccines are made. The Sputnik V vaccine, made by Russia’s Gamaleya Research Institute and the vaccine made by CanSino, a Chinese manufacturer, are made in the same way as the Johnson & Johnson and AstraZeneca vaccines.

The four vaccines use modified adenoviruses — viruses that cause colds — to deliver instructions to human cells to make the SARS-CoV-2 spike protein, the exterior proteins that allow SARS-2 viruses to attach to and invade cells. Those vaccine-induced spike proteins teach the immune system to look out for and defend against SARS-2 viruses.


Theories about the cause of the rare clotting issues hinge on the possibility that, in small numbers of people, the adenoviruses trigger an aberrant immune response. That, in turn, results in a rare combination of widespread clotting and low platelet counts.

Top officials of the Food and Drug Administration and the Center for Disease Control and Prevention stressed during a press conference Tuesday that clotting problems have not been seen with the vaccines made by Moderna and the Pfizer-BioNTech partnership. Roughly 180 million doses of those vaccines have been given so far in the country.

Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, skirted around the term “class effect” but suggested the fact that the problem was also seen with the AstraZeneca vaccine underscored for the FDA and CDC that the events might be linked to vaccination.

“I hesitate to call it a class effect,” Marks said. “But I think it is plainly obvious to us already that what we’re seeing with the Janssen vaccine looks very similar to what was being seen with the AstraZeneca vaccine.”

Janssen is the name of Johnson and Johnson’s vaccines division.

The CDC and the FDA jointly conduct surveillance for adverse events that might be linked to use of vaccines; the two agencies jointly announced the recommendation that use of the vaccine be paused. The move falls short of an order not to use the vaccine and Marks acknowledged that it may continue to be used in some cases, if a provider and a patient discuss the risks and benefits and decide to proceed with vaccination.

The CDC’s Advisory Committee on Immunization Practices, which advises the public health agency on vaccine uses, is holding a special meeting Wednesday to review the J&J data. It is conceivable that the panel of outside experts will suggest that use of the vaccine be continued, but with some restrictions on who should get this vaccine. A number of other countries in Europe and elsewhere have already imposed such limits on use of the AstraZeneca vaccine. That vaccine has not been authorized in the United States.

The FDA and CDC officials stressed the decision to pause use of the J&J vaccine was made “out of an abundance of caution.” Key to the decision was recognition of the need to inform health care providers to be on the lookout for people who might be having one of these reactions so that they can avoid giving care that could make the situation worse.

“The issue here with these types of blood clots, is that if one administers the standard treatments that we as doctors have learned to give for blood clots, one can actually cause tremendous harm or the outcome can be fatal,” Marks said. “One needs to make sure that providers are aware that if they see people who have low blood platelets, or if they see people who have blood clots, they need to inquire about the history of recent vaccination, and then act accordingly.”

In a statement, Johnson & Johnson said it is working closely with health authorities and medical experts to investigate the issue. It also announced it would delay the rollout of its vaccine in Europe.

Neither the statement from the agencies nor the statement from the company referenced the status of Johnson & Johnson’s ongoing clinical trial in the United States that is testing its vaccine in a two-dose regimen. The vaccine is currently authorized for use in a single dose.

When asked if the company has been asked to pause the trial, Marks said statements from the company would address voluntary actions the company is taking. J&J did not immediately respond to a request for comment from STAT.

The blood clots reported in the six cases are known as cerebral venous sinus thrombosis (CVST); in all cases, the clots were seen in combination with low levels of blood platelets, a condition known as thrombocytopenia. All occurred among women between the ages of 18 and 48, the statement from the CDC and FDA said, and symptoms occurred between six and 13 days after vaccination. In addition to the fatal case, one of the women is in critical condition.

Experts applauded the decision as the right thing to do.

“The pause is a prudent step to take, because when very serious adverse events occur that are also very rare, what matters most is ‘very serious,’” said John Moore, an immunologist at Weill Cornell Medicine. “Not only are individual members of the public at some risk, but so is the wider confidence in the Covid-19 vaccines.”

“It’s a reasonable but unproven assumption that the J&J and AstraZeneca vaccine safety concerns are linked by being related to an immune response against an adenovirus component,” he said. “So, FDA and scientists need time to better understand what is going on, which means a pause is the right course of action.”

But another expert acknowledged that the news may threaten the vaccine’s future use in this country.

“You have a greater chance of being in a car accident on the way to getting this vaccine than you have of having a problem from this vaccine. But that’s not how people view risk,” said Paul Offit, a vaccine expert at Philadelphia Children’s Hospital.

“In this country, you have two other vaccines, which are likely going to be produced in a quantity that enables everyone to be vaccinated,” he said. “So I think as we get more and more of the Moderna and Pfizer vaccine out there … I think it would not be surprising if … this vaccine would not come back onto the market.”

Offit was on the advisory panel that recommended the FDA authorize use of Johnson & Johnson’s vaccine.

The CDC and FDA said people who have received the Johnson & Johnson vaccine who develop certain symptoms within three weeks of receiving the vaccine should contact their health care provider. The symptoms were listed as severe headache, abdominal pain, leg pain, or shortness of breath.

The investigation into the Johnson & Johnson vaccine comes at a critical time for the Covid-19 vaccine rollout. Vaccine supplies that were scarce earlier in the year are starting to swell; rather than long lines, some jurisdictions are starting to report having unclaimed shots.

That had been expected. It has been known that behind the hordes desperate to be vaccinated was some significant portion of people who were worried about getting newly developed vaccines as well as some who will refuse vaccine under all circumstances. Persuading the former to get vaccinated in the face of a reports of a potential link between some of the Covid vaccines and a serious side effect will increase the challenge.

That said, vaccination with the AstraZeneca vaccine continues in many countries, though a number have placed limits on who can receive the vaccine — reserving its use for older adults, in whom these events have not been reported.

In Europe, where the AstraZeneca vaccine is being widely used, at least 222 suspected cases have been reported among 34 million people who have received the vaccine, according to a news report in the journal Science.

  • I got this J&J vaccine but i did not have problem even most of my friends in Virgina
    it might the person had some allergy with Vaccine so just FDA and CDC
    investigate and let J&J vaccine back to market. i

  • Although relatively rare, clotting and stroke issue is a common problem for adenovirus based Covid vaccines: AstraZeneca, J&J, Sputnik V and Cansino.

    But the much bigger problem is their efficacy. For example, “milder” Covid cases were sometimes not counted. These milder cases often led to long Covid neurological problems, brain fog, chronic fatigue, vision problems, etc. Counting these cases, the efficacy is likely only ~60%.

    Therefore ~40% can still break through the vaccine induced immune defense.
    40%*10 Million people = 4 Million infections
    ~30% will have significant health problems
    30%* 4 Million = 1.2 Million people’s health can still be compromised

    Note: For countries without much access to various vaccines, 60% protection is still far better than 0%.

    Moderna, Biontech, CureVac and Novavax are clearly superior in both efficacy (>90%) and safety. The much higher antibody levels also made them more effective against the variants.

    The rapid rise of variants (e.g., UK variant became the dominant strain in the US and EU in just ~2 months) have to be closely monitored worldwide using gene sequencers by Illumina and Pacific Bioscience. Other new variants (from India, Middle East, Russia, Japan) will soon come up during next 3 months. mRNA vaccines can then rapidly code for these newly sequenced variants to keep them in check.

    • Doctor – I am a layman but understood the situation exactly as you stated it, but I am interested in your opinion as to exactly how long it will be before the mRNA vaccines which have been modified to stop the variants will become available.

      I saw a claim Moderna will have a vaccine update by the end of the year. Do you think that will prevent a future outbreak? I think the big outbreak will happen this summer, IF some of the variants escape vaccine induced immunity. And we keep getting mixed reports – the mRNA vaccines stop the South African variant – then they don’t. I am very scared by the Brazilian type which seems to be much more dangerous, much more contagious, and to definitely reinfect people who were sick less than a year ago.
      Do we need to speed up the development of variant vaccines?

    • Good points and valid concerns, Steve.
      Moderna has developed a new version for the S. African variant.
      I think Biontech and CureVac should develop for the Brazilian variant. mRNA vaccines can be tuned in a few weeks.

      My prediction is that the next major variants will be most likely from India, Turkey/Iran and Indonesia/Philippines.

      We should immediately double or triple viral genetic sequencing, and increase to 10 times by the end of the year. Aim to have genetic sequencers in cities and major hospitals in US, EU and around the world to have real time pulses of the viral mutations.

  • The minuscule nature of this risk isn’t being properly communicated to people. The chance of getting hit by lightning in any year is about 1 / 500,000 , over twice the risk of getting a blood clot.

    The base rate of blood clots in the general population has increased from COVID-19 (2% of COVID-19 patients who go to a doctor get blood clots). In Germany they didn’t take that into account, and I somewhat doubt the CDC/FDA did either.

    Banning the vaccine and halting the rollout was the wrong move by the FDA. They have. They have suffered massive reputational damage as a result as it makes it look like the vaccine is unsafe, which it is not. Or at least it’s not any less safe then things people do all the time like driving or drinking alcohol.

    • What if they are not being honest about the reason? What if the Johnson and Johnson vaccine is less effective against some of the variants (which I see reported) than the mRNA vaccines, and they have decided it will be harder to get people vaccinated with a JJ shot now, and a variant update later, than to give them two mRNA shots now?

      What I see from Dr. Fauci has been, he has not been forthcoming about his reasons for doing things. He started recommending double masking, and after an uncomfortable exchange with Sen. Rand Paul, where Paul said it was theater, Dr. Fauci eventually said the variants were the reason for increased caution – Sen. Paul went into there being no proof of the danger from the variants – that seemed pretty lame to me – the thing to do would have been to pursue why Dr. Fauci was so worried about the variants.

      Maybe Dr. Fauci is very worried about the variants – which are reported to be 3 times more lethal to young people, 2 times more lethal to older folks and at least 2 times more contagious – AND to clearly escape natural immunity (Brazil P1), and, though there is some evidence P1 escapes the mRNA vaccines, so far it seems better than JJ.

    • I should add in – Dr. Fauci has said very definitely he does not want to go to the delayed 2nd dose schedule for mRNA vaccines which the UK has been using, and his specific reason has been fear a person with one dose may have just enough immunity to remain infected, and give the virus time to mutate to become more pathogenic. There was a paper claiming this happened in one immune impaired patient.
      So, giving out a vaccine which is not very effective against a variant would also worry Dr. Fauci, I believe. I think he has said that directly about the mRNA vaccines, and may be similarly worried about the JJ vaccine.
      Obviously, this is speculation but again and again we see him not telling us what he is thinking, so….??

    • Sorry for so many comments – but in my last comment, the paper said an immune impaired patient had a long infection which ended with a new variant developing in that one patient’s body – I did not mean to say that patient got one does of an mRNA vaccine – this was before they were available I think. Sorry again.


    This announcement is made by CanSino Biologics Inc. (the “Company”) on a voluntary basis.

    The Company has noticed certain media reports related to reported cases of a rare and severe type of blood clot in individuals after receiving AstraZeneca (AZ) COVID-19 vaccine and Johnson & Johnson (J&J) COVID-19 vaccine.

    The Company hereby provides the shareholders and potential investors of the Company with the following information:

    The vector of the Recombinant Novel Coronavirus Vaccine (Adenovirus Type 5 Vector)(the “Ad5-nCoV”) is Adenovirus Type 5 Vector, one of the commonly infective human adenovirus types, which is different from ChAdOx1 and Adenovirus Type 26 Vector, the respective vector of AZ COVID-19 vaccine and J&J COVID-19 vaccine.
    As at the date of this announcement, no blood clot related serious adverse events have been reported in around one million vaccinations of Ad5-nCoV.
    The Company will closely monitor the situation and make further announcement(s) as and when appropriate in this regards in accordance with the requirements of the Rules Governing the Listing of Securities on The Stock Exchange of Hong Kong Limited.
    By Order of the Board

    CanSino Biologics Inc.

    Xuefeng YU

  • Could some of the post effects for clot formation be because people have undiagnosed, underlying hypercoagulation disorders? We’re studies done on people who have a history of clothing disorders, arterial fibrillation, on blood thinners?

  • The clotting and stroke issues are relatively rare ~ 1 in 100K. But the rate is higher than other Covid vaccines.

    I agree with the author Madame Helen that “class effect” — “a problem one would expect to see with all vaccines made in the way the J&J and AstraZeneca vaccines are made. The Sputnik V vaccine, made by Russia’s Gamaleya Research Institute and the vaccine made by CanSino, a Chinese manufacturer, are made in the same way…” As many are aware of, Russia and China have not been that open and transparent about their data.

    I very much agree with Dr. Offit that although this is a low risk, J&J and AstraZeneca vaccines will most likely be put into cold storage in USA and EU. Will later be given to desperate countries, as they will not get Moderna, Biontech/Pfizer and Novavax soon enough.

    “You have a greater chance of being in a car accident on the way to getting this vaccine than you have of having a problem from this vaccine. But that’s not how people view risk,” said Paul Offit, a vaccine expert at Philadelphia Children’s Hospital. “… I think it would not be surprising if … this vaccine would not come back onto the market.”

    • My husband and I did a lot of reading and research before we both agreed that the J & J vaccine was the best choice for our family. We’re both type 2 diabetics (inherited) and I have a congenital heart condition. Neither of us have had any complications or side effects from the vaccine. My thoughts lean towards the possibility of in the rare small cases of these clotting issues is whether or not the patients had underlying conditions that could’ve made them susceptible to such a problem? The majority of the vaccines distributed shows more positive results than the negative so I’m wondering what else could be a cause.

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