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Study finds heart conditions extremely rare after COVID-19 vaccination

Study finds heart conditions extremely rare after COVID-19 vaccination

  • A Canadian examine demonstrates that myocarditis and pericarditis immediately after COVID-19 mRNA vaccinations are particularly uncommon.
  • This exploration also indicates that spacing out second doses to 30 times and providing Pfizer vaccines about Moderna might lessen the hazard of acquiring these circumstances in males ages 12-29.
  • Professionals anxiety that acquiring COVID-19 poses a greater hazard of myocarditis and pericarditis than staying vaccinated.

Specialists at the College of Alberta in Canada have analyzed evidence on the danger of myocarditis and pericarditis just after COVID-19 vaccination and observed the risk is low, which includes among the younger gentlemen. These conditions, typically prompted by viral infections, contain irritation of coronary heart tissues.

The results do ensure that the challenges manifest extra commonly between younger males soon following a next dose of the mRNA vaccine.

Most scenarios have been mild, and the danger appears to be greater immediately after getting Moderna’s mRNA vaccine than Pfizer’s counterpart.

The researchers propose that applying Pfizer above Moderna and spreading out dosing intervals may cut down hazards for young people.

This study seems in the BMJ.

Myocarditis refers to the swelling of the heart muscle mass, and pericarditis occurs when there is inflammation of the sac surrounding the coronary heart. Both of those disorders are usually caused by a viral infection.

The ailments are unusual but critical. Fortunately, most people today thoroughly get better.

An uptick in circumstances following COVID-19 mRNA vaccinations has produced concern among the healthcare and public health leaders.

Reports to start with appeared in April 2021, main to monitoring aspect results after vaccination with Pfizer and Moderna’s mRNA vaccines.

Pediatric and coronary heart professionals at the University of Alberta analyzed over 8,000 cases immediately after combing through 46 studies.

They started investigating documents of men and women in each individual age team and zoned in on individuals -39 yrs of age. According to the scientists, incident charges in grownups ages 40 many years and more mature were “very minimal to none.”

How recurrent are they?

The researchers noted that the total fees of myocarditis are 1-2 scenarios for every 100,000 individual-yrs in the United States. Individual-years is a measurement made use of in future scientific studies in which scientists think about the amount of contributors associated and how significantly time each individual person spends in the review. If a analyze adopted 100 persons for 20 decades, the analysis would comprise 2,000 particular person-decades of knowledge.

The study located that costs of myocarditis immediately after COVID-19 vaccination are .2 for every one million persons — and 1.4 for each one particular million for pericarditis.

They discovered that adolescent and youthful grownup males experienced the maximum incidences of myocarditis following obtaining mRNA vaccines against SARS-CoV-2. The findings are in trying to keep with historical tendencies about this problem.

Male teenagers ages 12-17 yrs had 50-139 instances per million, and male older people ages 18-29 experienced 28-147 scenarios for each million.

Moderna vs. Pfizer

Health-related Information Now discussed this analyze with Dr. Jorge Moreno, an assistant professor of medication at the Yale School of Medication. He was not included in the examine.

Dr. Moreno agreed that scenarios of COVID-19 vaccine-associated myocarditis and pericarditis are rare.

He also stressed that “COVID, the sickness, can also [cause] myocarditis, and that is considerably more possible than the vaccine alone [causing it].”

Dr. Moreno mentioned that some European nations favor the Pfizer COVID-19 vaccine, which appears to carry a reduced chance of myocarditis than the Moderna vaccine.

On the other hand, he included, “the Fda and the CDC below in the U.S. did not find that the change was significant more than enough to make that suggestion.”

Improve dosing plan?

The scientists also identified that the threat of myocarditis or pericarditis might be decreased if people today receive their next vaccine dose much more than 30 days immediately after the very first.

Data precise to young males indicates that growing dosing intervals to above 56 times may perhaps substantially lessen rates of the problems.

Dr. Moreno felt that far more experiments are wanted to evaluate the plan of spacing vaccine doses.

At this time, the Earth Health and fitness Firm (WHO) does not suggest that men and women underneath 18 receive a booster shot.

The authors stressed that facts for danger aspects had been restricted. They hope that foreseeable future experiments will involve tissue samples and long-phrase follow-up to “enhance comprehending of mechanism[s]” driving the coronary heart situations.

The COVID-19 landscape is promptly modifying, contacting for frequently evolving exploration.

In a joined editorial, some U.S. researchers pointed out that threats relevant to boosters and vaccinating youthful little ones stay unclear. The lengthy-expression results of folks who create myocarditis are also yet to be comprehended.

MNT also spoke with Dr. Jeffrey J. Hsu, a cardiologist at UCLA Wellbeing, concerning the current analyze. He was not associated in the research.

Dr. Hsu stated he is nervous that myocarditis and pericarditis problems may have deterred some persons from having vaccinated:

“While scientific studies this kind of as this a single demonstrate that these problems do come about not often following vaccination, my problem is that the results of these scientific studies are either misinterpreted or distorted when communicating them to the public.”

Dr. Hsu and Dr. Moreno emphasized that relaying info with empathy will make the most efficient technique for encouraging the vaccine-hesitant.

Dr. Hsu stated: “We have significantly far more information on both the positive aspects and dangers of vaccination now when compared to previously in the pandemic and it is vital for clinicians to plainly connect our newest being familiar with of the effects of vaccination. Also, for patients who are hesitant to carry on with vaccination, I have identified it valuable to expend the time to recognize their distinct reservations.”

Cultural challenges

Dr. Moreno spelled out why some persons remain unaware or skeptical of the success and protection of vaccines.

For instance, a appreciable proportion of the Hispanic population faces a language barrier. The assistant professor additional: “I consider that there is a large amount of mistrust in the healthcare method from several years of challenges that have appear up, irrespective of whether it is finding access to health care [or] insurance coverage challenges.”

Dr. Moreno also said achieving numerous Hispanic and Black people today demand a further being familiar with of cultural variances.

Dr. Hsu commented: “For some people today, it is apparent that nothing at all will improve their stance on vaccination, though many others may possibly just be trying to find clearer facts from a reliable source, these as their medical doctor.”

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Monkeypox: CDC monitors 6 people in US for possible rare infection, says public ‘should not be concerned’

Monkeypox: CDC monitors 6 people in US for possible rare infection, says public ‘should not be concerned’

At present, the CDC is monitoring six men and women in the United States for probable monkeypox infections just after they sat in the vicinity of an infected traveler who had signs even though on a flight from Nigeria to the United Kingdom in early May well.

Individually, CDC officers also are investigating a circumstance of monkeypox confirmed in a gentleman in Massachusetts who had lately traveled to Canada. And in New York Metropolis, just one individual has examined favourable for orthopoxvirus, the loved ones of viruses to which monkeypox belongs, NYC health officials introduced in a information release Friday.

The circumstance is remaining addressed as a “presumptive good” situation till verified pending CDC tests and the affected person is at the moment isolating, the release states.

New York Condition Health and fitness Commissioner Dr. Mary T. Bassett explained in a assertion Friday that “the present risk to the community is very low.”

“Reviews of suspected cases of monkeypox in the United States and elsewhere are about. Although a achievable scenario in New York Point out awaits confirmatory tests by our local and federal partners, the Section has alerted overall health treatment companies in New York Condition so that they can take into consideration this abnormal diagnosis if their sufferers current with symptoms,” Bassett mentioned.

CDC and Massachusetts health officials investigating monkeypox case

Meanwhile, current monkeypox infections have been recognized in many other areas about the environment the place the virus is not normally prevalent, such as Canada, Excellent Britain, Italy, Northern Ireland and Spain.

“We have a degree of scientific worry about what we’re seeing due to the fact this is a extremely unconventional predicament. Monkeypox is normally only noted in West Africa or Central Africa, and we you should not see it in the United States or in Europe — and the number of scenarios that are currently being claimed is definitely outdoors the degree of typical for what we would see,” Jennifer McQuiston, deputy director of the Division of High Consequence Pathogens and Pathology within the CDC’s Nationwide Centre for Emerging and Zoonotic Infectious Health conditions, informed CNN on Thursday.

“At the same time, there seriously usually are not that a lot of instances that are staying claimed — I feel possibly a dozen, a few dozen — so, the basic general public really should not be anxious that they are at immediate possibility for monkeypox,” she said. “We’re operating through the investigations.”

Total, “we have people today who are being monitored for disorders all the time,” CDC spokesperson Christine Pearson wrote in an electronic mail, Thursday. That usually means that if somebody could have been exposed to a pathogen, their well being is monitored, and they need to see physicians if they acquire signs and symptoms.

As for the 6 people at the moment currently being monitored for opportunity monkeypox, they all “are nutritious, with no signs and symptoms and are thought of at low risk for monkeypox,” Pearson wrote, adding that none ended up seated next to the ill passenger and none had immediate get in touch with.

As the CDC’s investigation proceeds, conversations have commenced to include the matter of vaccines.

CDC ‘discussing and evaluating’ smallpox vaccine

CDC officials are analyzing irrespective of whether smallpox vaccine really should be available to health care personnel dealing with monkeypox patients and other people today who may perhaps be at “large chance” for exposure to monkeypox, McQuiston said.

“It is absolutely anything that we’re talking about and evaluating, whether presenting smallpox vaccine makes sense in the present-day environment,” she reported. “We’ll be nearer to generating suggestions for that in the upcoming working day or so.”

The variola virus that will cause smallpox and the monkeypox virus are to some degree related as they are both of those members of the Orthopoxvirus genus, belonging to the scientific loved ones of “pox” viruses. For that reason, some of the exact vaccines administered to prevent smallpox have also been revealed to prevent monkeypox. Even however the viruses are related, monkeypox is a lot less contagious than smallpox and causes a lot less critical condition.

“We have vaccines that are stockpiled and readily available to be employed, and if judged as a way to help manage this outbreak, we have the availability to use them,” McQuiston explained.

“I would say that we are in the early days of knowing what is leading to this outbreak — and the truth that we are looking at situations described in various sites around the globe indicates that perhaps it really is been likely on for a few of weeks,” she mentioned. “As we work to total our investigations and get our arms all-around it then ideally we will have much stronger tips for people.”

Monkeypox, a viral ailment, is scarce in the United States and the virus does not happen naturally in the nation, according to the CDC. But instances have been identified that have been affiliated with international travel or importing animals from locations wherever the sickness is more frequent. Soon after the virus jumps from an animal to a human, human-to-human transmission of monkeypox can manifest when a man or woman encounters the virus via direct call to: massive respiratory droplets, bodily fluids, or lesions on the pores and skin.
Monkeypox signs and symptoms can involve fever, headache, muscle mass aches and swollen lymph nodes. A characteristic of the condition is that it can bring about lesions and a rash on the body, together with the palms of the arms and the soles of the toes.

“This is not a condition that is heading to sweep throughout the place,” Dr. Daniel Bausch, president of the American Society of Tropical Medicine & Hygiene, told CNN on Thursday.

“From a general public health angle, of study course, we need to examine and respond — I believe the common population need to just be conscious of this — but you can find surely no rationale to panic and I feel it is really, highly, remarkably unlikely that we will get any type of huge outbreak of this,” he reported. “And if you have not had get in touch with in Massachusetts and you are not similar to the particular person who experienced sickness or in that website link at all — till we have any other purpose to assume or to understand how this disorder bought into the United States — your risk of receiving monkeypox is really lower.”

A monkeypox mystery

In Massachusetts, doctors donning the very same personal protecting devices they put on for Covid-19 people have been managing the US monkeypox affected individual at a unique pathogens device inside of Massachusetts Common Clinic, where by he initially was diagnosed.

“They were undergoing a workup linked to signs and the infectious illnesses health practitioner observing the client, discovering about some of the instances in the United Kingdom, determined that the individual could maybe have monkeypox,” Dr. Erica Shenoy, healthcare director for the Regional Rising Exclusive Pathogens Procedure Centre and affiliate chief of the infection manage device at Massachusetts Basic Hospital, advised CNN on Thursday.

“Then we had discussions with our state community well being officers. The decision was produced that certainly, they did meet up with criteria for screening,” Shenoy reported. The affected individual tested constructive.

“I assume to the public overall, there definitely is no clear danger at this point,” Shenoy stated. “This is an evolving situation that we are wanting to understand improved — why these clusters that have been described as well in the Uk and in Portugal and Spain are occurring, and to superior understand the epidemiology.”

Each in the United Kingdom and Canada, well being authorities have pointed out that quite a few of the monkeypox cases had been discovered in males who have sex with adult males — but the virus is not commonly described as a sexually transmitted infection and investigations into these latest circumstances continue.
Rare case of monkeypox reported in England, UKHSA says
Monkeypox was 1st discovered in 1958 when two outbreaks of a pox-like sickness were viewed in colonies of monkeys that ended up held for research, top to the title “monkeypox,” according to the CDC. The very first human situation of monkeypox was noted decades later in 1970 in the Democratic Republic of Congo, all through a time when rigorous attempts ended up underway to do away with smallpox.
In the United States, the last outbreak of monkeypox recorded was in 2003, when 47 verified and probable instances were being reported in six states: Illinois, Indiana, Kansas, Missouri, Ohio and Wisconsin. “No scenarios of monkeypox an infection have been attributed completely to man or woman-to-individual get hold of,” in accordance to CDC.

All of the people today contaminated with monkeypox during that outbreak grew to become ill just after obtaining call with pet prairie dogs, the CDC observed. Individuals pets ended up housed at an animal vendor’s amenities in Illinois wherever they could have been infected with the virus. The amenities housed other compact mammals imported from Ghana that analyzed good for monkeypox virus: two African big pouched rats, 9 dormice and a few rope squirrels.

“The prairie dogs obtained monkeypox from the imported animals and then passed it on to the individuals,” Bausch reported. “It’s a bit of a misnomer calling it monkeypox. The reservoir for this virus, the purely natural reservoir in mother nature is likely specific sorts of rodents.”

US Surgeon Basic Dr. Vivek Murthy explained Thursday that folks really should not be concerned about monkeypox at this issue, but that they should really be mindful of signs and symptoms and when to arrive at out for support.

Murthy described on CNN’s New Day that monkeypox is scarce in humans, “but when it does arrive up, it is really a critical a person that we really should look into, and we’ve got to make sure that we understand if and how it is spreading from man or woman to particular person.”

Signs or symptoms usually are similar to the flu, he told CNN’s John Berman and Erica Hill.

“The great information is we have a person verified situation appropriate now. But we ought to often be on the lookout for extra situations,” he explained. “At this time, we will not want persons to fret. At this place, yet again, these numbers are continue to tiny — we want them to be conscious of these symptoms and if they have any worries to get to out to their medical professional.”

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AstraZeneca, Pfizer, and rare blood clots

AstraZeneca, Pfizer, and rare blood clots

Someone wearing rubber gloves pulling a bottle of AstraZeneca vaccine from its boxShare on Pinterest
Do COVID-19 vaccines increase blood clot risk? HANNIBAL HANSCHKE/Getty Images
  • Two large studies have found a small increase in the absolute risk of rare types of blood clot in the head following a first dose of the AstraZeneca COVID-19 vaccine.
  • An increased risk of a type called intracranial venous thrombosis only applied to individuals under 70 years of age.
  • The benefits of vaccination to protect against severe COVID-19 far outweigh the risks that the researchers identified.
  • They found no evidence of increased risks following a first dose of the Pfizer-BioNTech COVID-19 vaccine.

In late February 2021, several reports emerged of rare types of “thromboses” — blood clots that block veins or arteries — after the AstraZeneca (ChAdOx1-S) COVID-19 vaccine.

The clots were in unusual locations, such as the veins in the head, and often accompanied by low platelet levels in the blood.

However, because the number of reported cases was so small, it has been difficult to estimate the increased risk for populations as a whole.

Scientists were also unsure whether the risk of common types of thrombosis also increases.

Part of the problem was that when COVID-19 vaccines became widely available, governments prioritized clinically vulnerable and older people, who are already more prone to thromboses.

In addition, publicity about the risk of blood clots after vaccination may have made doctors more likely to diagnose thromboses. This would give a false impression that they had become more common.

Two studies that pooled data for millions of patients in the United Kingdom have now found a small increase in the absolute risk of rare types of blood clot in the head. There was no evidence of any increased risk of more common types of blood clot.

“We were worried that there might be more thromboses diagnosed in people after the complications of the AstraZeneca vaccine had been reported,” explained Dr. William Whiteley, Ph.D., of the Centre for Clinical Brain Sciences at the University of Edinburgh in the U.K., and the lead author of one of the studies.

“This was the reason we did the study using data from before the date the thrombotic complications of the AstraZeneca vaccine were widely reported,” he told Medical News Today.

“But our estimates [of the frequency of blood clots], and those done afterward are similar, so this may not be such a concern,” he added.

In the U.K., a vaccination program that employed the Pfizer-BioNTech vaccine began on December 8, 2020, with the AstraZeneca vaccine added on January 4, 2021.

The program prioritized extremely clinically vulnerable individuals and those over 70 years, followed by people with chronic illnesses, such as diabetes and high blood pressure, and those over 65 years.

In the first study, researchers led by Dr. Whiteley analyzed the electronic health records of 46 million adults in England, 21 million of whom had their first vaccine dose between December 2020 and March 2021.

Overall, 79{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} of the participants were white, 51{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} female, and 84{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} under 70 years.

The researchers compared the incidence of thromboses before and after the first dose of vaccine. They then adjusted the figures to account for other factors that might affect the incidence of blood clots, including age, sex, ethnicity, socioeconomic status, existing medical conditions, and medications.

After adjustments, the overall risk of thromboses was lower in the 28 days after the first dose of either the AstraZeneca or Pfizer-BioNTech vaccine, compared with before vaccination.

For AstraZeneca, the risk of thromboses in veins was 3{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} and 42{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} lower in those under 70 and those 70 years or older, respectively. The risk of thromboses in arteries was 10{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} and 24{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} lower, respectively, in these age groups.

The corresponding figures for the Pfizer vaccine were 19{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} and 43{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} lower for thromboses in veins, and 6{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} and 28{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} lower for thromboses in arteries.

The researchers believe that the most likely explanation for these improvements is that vaccination substantially reduced the likelihood of COVID-19, which can itself cause thromboses, especially in the lungs.

In people under 70 years of age, the rates of intracranial venous thromboses — blood clots in a vein in the head — or hospitalization with low platelet levels were roughly twice as high in the 28 days after a first dose of the AstraZeneca vaccine.

However, because these events are extremely rare, the absolute increase in the number of events was very small.

The scientists estimate that after adjustments for other risk factors, the AstraZeneca vaccine may cause between 0.9 and 3 extra cases, depending on age and sex, for every million people vaccinated.

This small increase in risk is easily offset by the reduced risk of becoming sick or dying from COVID-19 that the vaccine provides.

“Most people want accurate information about the pros and cons of the treatments that they take, and we are providing information for them,” said Dr. Whiteley.

“The overwhelming majority of people in the U.K. decide to be vaccinated against COVID-19 when offered a vaccine, and because of this COVID-19 is less of a threat to us all,” he added.

After a first dose of the AstraZeneca vaccine, the study found no increase in the risk of intracranial thromboses among people 70 years or older.

Following a first dose of the Pfizer vaccine, there was no increased risk either for people older or younger than 70.

The results of the study appear in PLOS Medicine.

The authors concluded:

“For older populations, who are most vulnerable to COVID-19, we found no evidence of increased risk of any event with ChAdOx1-S. In younger populations, who have a lower morbidity and mortality due to COVID-19, other available vaccines might be prioritized, especially when the risk of COVID-19 is otherwise low.”

The scientists plan to publish results of their analyses of blood clots after second vaccine doses, and after COVID-19 infections, in future papers.

In the second study, scientists led by the University of Edinburgh in the U.K. investigated the incidence of a rare type of blood clot in the brain called cerebral venous sinus thrombosis (CVST).

In 2021, several countries withdrew the AstraZeneca vaccine or restricted its use to older people following initial reports of a possible link between the vaccine and CVST.

The background incidence of CVST is only 3 to 4 per million person-years in adults, but the chances of dying for someone with a CVST is around 4{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809}.

Dr. Steven Kerr, Ph.D., a senior data scientist at the University of Edinburgh, and his colleagues linked electronic medical information from primary care and secondary care, plus mortality and virological test data.

The study encompassed data from more than 11 million people in England, Scotland, and Wales who received their first dose of a COVID-19 vaccine from December 2020 through June 2021.

The researchers compared the rate of CVST events for individuals during a 90-day period before their vaccination with the 4 weeks afterward.

This is known as a self-controlled case series, where individuals act as their own control to account for other possible risk factors that they might have that are unchanging over time.

There were 201 CVSTs in total. Out of these, 81 CVSTs occurred in the follow-up period after the first dose of the AstraZeneca vaccine, or 16.34 events per million doses.

This represents a doubling of the very low initial incidence of CVST, which equates to one extra event for every 4 million people vaccinated.

There were 40 CVSTs among those who received a first dose of the Pfizer vaccine, or 12.6 events per million doses.

This suggests that there is no link between the Pfizer vaccine and CVST.

The study appears in PLOS Medicine.

“It is important to understand that CVST is an extremely rare event, which typically only occurs a handful of times per million people per year,” Dr. Kerr told MNT.

“This should be weighed up against the risk associated with contracting COVID and the level and duration of protection that vaccines offer,” he said.

He added that the relative increase in the risk of CVST following a first dose of the AstraZeneca vaccine may be higher in young people than in older people.

“This is something we may be able to study in the future as we amass data that covers a longer time period,” he added.

The authors say they will use the same methodology to investigate any possible risks of CVST with the Moderna vaccine, which is now also in use in the U.K., and the second and booster doses of all three vaccines.

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CDC recommends Pfizer and Moderna vaccines over Johnson & Johnson due to rare blood clotting issue

Dr. Janette Nesheiwat on Johnson & Johnson vaccine

The CDC now recommends that Americans take the mRNA vaccines made by Pfizer and Moderna instead of the one-shot Johnson & Johnson vaccine due to rare but serious blood clots.

The agency’s Advisory Committee on Immunization Practices unanimously voted on Thursday to give a preferential recommendation to Moderna and Pfizer’s shots. 

“More than 200 million Americans have completed their primary vaccine series, providing protection against COVID-19, preventing millions of cases and hospitalizations, and saving over a million lives,” CDC Director Rochelle Walensky said in a statement. “Today’s updated recommendation emphasizes CDC’s commitment to provide real-time scientific information to the American public.”

The CDC temporarily halted Johnson & Johnson’s vaccine in April while scientists investigated the blood clots, which are known as “thrombosis with thrombocytopenia syndrome.”

Syringes filled with the Johnson & Johnson vaccine are shown, Thursday, May 13, 2021, at a mobile vaccination site at the Greater Bethel Church in Miami. ((AP Photo/Wilfredo Lee))

Regulators eventually decided that the benefits of the Johnson & Johnson vaccine outweighed the risks, but the FDA released new data this week showing that more cases have occurred in the summer and fall. 

Women between the ages of 30 and 49 are most affected by the blood clotting issue at a rate of about 1 in 100,000 shots. 

Health officials have confirmed 54 cases of the blood clots, nine of which have been fatal, CDC official Dr. Isaac See said Thursday. Two more deaths are suspected to be related to the blood clotting issue. 

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A CDC official told FOX Business that individuals who received the Johnson & Johnson vaccine should still receive a booster dose two months after their initial vaccine. 

If an individual received a Johnson & Johnson shot for their primary dose and then a booster of any vaccine, then they do not need to be re-vaccinated with an mRNA COVID-19 vaccine, according to the official. 

Michelle Falgout, a registered nurse, administers a dose of the Johnson & Johnson COVID-19 vaccine to Kerri Houston at a Florida Department of Health in a Pinellas County vaccination event held at the Salvador Dali Museum in St. Petersburg, Flori

Symptoms of blood clots – including severe headaches, abdominal pain, back pain, and nausea – usually occur 6 to 14 days after receiving the Johnson & Johnson vaccine, according to the American Society of Hematology. 

Only about 16 million doses of the Johnson & Johnson vaccine have been administered in the United States, compared to about 470 million doses of the vaccines made by Pfizer and Moderna. 

COVID-19 VACCINE EFFECTIVENESS WILL LIKELY DROP AGAINST OMICRON VARIANT, MODERNA CEO SAYS

The Johnson & Johnson vaccine is a viral vector vaccine, meaning that it replaces a small piece of the genetic instructions in a harmless adenovirus with genetic instructions for the SARS-CoV-2 spike protein. When the vaccine is injected, our cells recognize that the spike protein isn’t supposed to be there and produce antibodies to fight it. 

Liesl Eibschutz, a medical student from Dartmouth University, loads a syringe with Pfizer COVID-19 vaccine before giving it to people on the first day that people ages 16 and up can receive the vaccine at Kedren Health on Thursday, April 15, 2021 in

AstraZeneca’s COVID-19 vaccine, which was produced in the United Kingdom, is also a viral vector vaccine and has led to similar blood clotting issues. 

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Several other countries have already recommended mRNA vaccines over the viral vector vaccines, or set age limits for the Johnson & Johnson and AstraZeneca vaccines. 

COVID-19 itself can also cause blood clots. The risk of developing cerebral venous thrombosis or portal vein thrombosis is “significantly increased after COVID-19,” according to a University of Oxford study in April. 

The Associated Press contributed to this report.