Watch: Insider answers your questions about the risk of rare but serious blood clots following some COVID-19 vaccines

COVID-19 vaccines from AstraZeneca and Johnson & Johnson are under close scrutiny following reports of rare blood clots in people who received them.

AstraZeneca’s vaccine has been linked with unusual blood clots that can occur in the brain, called central venous sinus thrombosis (CVST), or in the spleen. EU regulators now list these reactions as a rare, but serious side effect of AstraZeneca’s vaccine.

The US hasn’t authorized AstraZeneca’s vaccine yet, but countries that have approved it are now weighing the small risk of blood clots against the shot’s many advantages. The UK has advised people under 30 to seek alternate shots, if available.

AstraZeneca’s shot is still highly effective at preventing severe COVID-19. It’s also fairly cheap and can be stored at normal fridge temperatures, making it a critical part of the global vaccine rollout.

J&J’s vaccine, which uses a similar virus-based technology, is under investigation in the US to see whether it also causes CVST. So far, US regulators have identified at least six CVST cases following the administration of J&J’s shot, and the shot’s use is paused.

European drug regulators are allowing the use of J&J’s shot again, after saying a warning about the risk of rare blood clots should be added to the shot’s product information.

J&J’s vaccine is a single dose, so it’s often easier to administer in rural areas or to vulnerable populations.

On Thursday, April 15, Insider health and science reporters Dr. Catherine Schuster-Bruce and Aria Bendix addressed what’s at stake for the pandemic in the wake of blood clot reports. They also answered your burning questions about who is most at risk of clots and whether other vaccines could cause adverse events, too.

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Don’t start doubting the Pfizer or Moderna vaccines – after 185 million doses, there are no red flags about blood clots

Pfizer COVID-19 coronavirus vaccine
A nurse prepares a shot of the Pfizer-BioNTech COVID-19 vaccine at Guy’s Hospital in London on December 8, 2020.

For the first time in the US’s vaccine rollout, regulators have pumped the breaks on an authorized coronavirus shot.

On Tuesday, the Centers for Disease Control and Prevention and the Food and Drug Administration together recommended a temporary pause in the distribution of Johnson & Johnson’s vaccine while regulators investigate six reports of unusual blood clots.

All six of those cases involved women between 18 and 48 who developed central venous sinus thrombosis, an exceedingly rare type of clot in the brain. One of the women died and another is in critical condition.

Experts aren’t sure why these blood-clot cases developed – or even if there’s a definite cause-and-effect relationship with the vaccine. But there’s no reason to suspect that rare clots would be associated with the US’s other authorized vaccines, they said.

“Instead of taking away confidence from other vaccines, this should actually inspire further confidence in the oversight of these vaccines and definitely should not deter individuals scheduled for either Pfizer and Moderna vaccines to go through with their appointments,” Dr. Vivek Cherian, an internal-medicine physician in Baltimore, told Insider.

Roughly 68 million American have been fully vaccinated with either Pfizer’s or Moderna’s shot since December, and nearly 185 million doses have been administered in total. In that time, US regulators haven’t discovered any significant safety concerns among people who’ve gotten those vaccines. (The CDC tracks vaccine side effects through a tool called V-safe and healthcare providers are required to report adverse reactions via an online system called VAERS.)

“There’s a lot of close scrutiny of these vaccines,” Peter Gulick, an associate professor of medicine at Michigan State University, told Insider.

He added that Pfizer’s and Moderna’s shots are “months ahead of J&J” in their production and rollout, and regulators have yet to see any red flags. Even his HIV patients, Gulick said, haven’t reported severe reactions.

J&J’s vaccine, by contrast, was introduced more recently: It was authorized in late February and has been administered to just under 7 million Americans so far.

“When you start vaccinating people, you have a much, much, much larger sample size – in the millions,” Cherian said. J&J’s clinical trial, by contrast, had just under 44,000 people. “So when you have these exceedingly rare complications, sometimes you don’t see that until you actually start.”

Pfizer’s and Moderna’s shots carry ‘virtually no risk’ of clotting

nurses vaccine
Nurse Janelle Roper, left, administers the Pfizer COVID-19 vaccine to fellow nurse Kate-Alden Hartman.

In an average year, just two to five out of every 1 million Americans develop central venous sinus thrombosis (CVST).

J&J’s vaccine hasn’t come close to exceeding these normal background levels yet, with fewer than one CVST case for every 1 million doses reported so far. But researchers have also seen some CVST cases among people who got AstraZeneca’s coronavirus vaccine, which bears many similarities to J&J’s.

By early April, European medical officials had identified 169 CVST cases out of more than 34 million people in the EU who’d received AstraZeneca’s shot. That’s still just five cases per 1 million shots, but it was enough for European regulators to conduct an investigation. The UK now recommends that people under 30 years old seek out other shots, if available.

Both AstraZeneca’s and J&J’s shot are viral-vector vaccines, which introduce a coronavirus gene into the body using a genetically engineered common-cold virus. Some scientists are wondering whether the platform itself could be linked to clotting.

Pfizer’s and Moderna’s vaccines, on the other hand, rely on mRNA technology, which uses a snippet of the coronavirus’ genome to trigger an immune response.

At an American Medical Association webinar on Tuesday, Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said the US has identified just three CVST cases among the 68 million people who got the double-dose mRNA vaccines.

In a Tuesday statement, Moderna also said it had carried out its own comprehensive analysis and found no association between its shot and CVST or other types of clotting.

“It’s safe to say there’s virtually no risk in individuals who received mRNA-based [vaccines], but we don’t really have that information yet as far as the viral-vector,” Cherian said.

But he added that even with the viral vector vaccines, “far, far less than even 1% of individuals are actually having these side effects.”

By comparison, a November study found that 20% of hospitalized COVID-19 patients developed blood clots in their veins.

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Why younger women have a higher risk of blood clots, whether or not they’re vaccinated

birth control pill
  • J&J’s COVID-19 vaccine distribution is paused after reports of 6 rare, severe blood clots.
  • The clots, seen with another blood condition, aren’t the same as those linked to birth control.
  • The birth control pill and pregnancy play into younger women’s higher risk of blood clots.
  • See more stories on Insider’s business page.

The US rollout of Johnson & Johnson’s COVID-19 vaccine is on pause as experts evaluate six cases of severe blood clots in the brain possibly linked to the shots.

It’s unclear if the vaccines lead to these clots or if it’s just a coincidence.

On one hand, the type of blood clot seen in conjunction with another blood condition in the six J&J cases is so rare in the general population its prevalence is unknown. That raises red flags that the shot could play a role.

On another hand, all six cases of post-J&J shot clots were in women between the ages of 18 and 48, a group at higher risk of blood clots anyway.

Similarly, most blood clot cases that occurred after AstraZeneca’s COVID-19 vaccine in Europe were in women under 55. The European Medicines Agency has said the shots themselves weren’t the cause.

Young women are at a higher risk of developing certain types of blood clots regardless of their vaccine status, Mary Cushman, a professor of medicine at the University of Vermont’s Larner College of Medicine, told Insider. Hormonal birth control and pregnancy may play a role in this elevated risk.

Birth control pills and pregnancy both increase the risk of blood clots

Young women are at a relatively high risk for blood clots since they’re most likely to take the birth control pill or get pregnant, which both increase the odds of developing a clot, Cushman told Insider.

Estrogen, a sex hormone that is in most oral contraceptives and spikes during pregnancy, is one reason for that elevated risk, Insider previously reported. The hormone has also been found to affect how immune cells respond to flu vaccines.

Specifically, the US Food and Drug Administration estimates that between 3 and 9 out of 10,000 women who take certain birth control pills will develop a blood clot each year, compared to 1 to 5 women per 10,000 who do not have risk factors for blood clots.

The risk of getting a blood clot as a side effect of the pill is higher than the likelihood of clotting due to the vaccine. Scientists have known about this risk factor for decades, however, it’s still rare, as a recent TikTok video pointed out.

“Millions of women everywhere take the contraceptive pill, and amongst the hundreds of side effects that come with the contraceptive pill – one of which is death – there’s a 6 in 10,000 chance of getting a blood clot,” TikToker alysselizabeth said in the video.

Still, the risk of clotting post-vaccine versus the risk related to birth control isn’t an apples-to-apples comparison. There’s far more data on birth control-associated clots, but a lot of it is flawed and outdated. Plus, the specific type of brain clots seen after J&J vaccine, as well as its presentation with low platelet count, differentiates them from the clots most typical among birth control pill users.

“This is a different clinical entity than blood clots associated with oral contraceptives,” Dr. Melanie Swift, co-chair of the Mayo Clinic COVID-19 Vaccine Allocation and Distribution Work Group, told Insider.

There are other risk factors for blood clots – including COVID-19

Obesity and genetic factors can also increase someone’s risk of developing a blood clot, Cushman said. Physical activity and other healthy lifestyle choices can help manage that risk.

“It’s always really important to stay active, avoid sedentary time, keep to a healthy weight, and have a healthy diet,” Cushman said. “And if you’re using an oral contraceptive, or if you have obesity, maybe just ratchet up your awareness a little bit, but don’t avoid the shot.”

She added that COVID-19 has been linked to deadly blood clots, too – so getting vaccinated will help prevent clots by lowering your chance of getting sick from the coronavirus.

“The bottom line is that the risk of adverse health consequences from COVID-19 far outweighs any risk of the shot,” Cushman said.

Added Swift: “I would tell everyone to have confidence in the vaccine safety monitoring system in the US. What an amazing feat to have detected a signal of only 6 people among millions. … We do not want this time out for one brand of vaccine to stall vaccination efforts overall because that would result in more needless lives lost to the pandemic.”

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Canada suspends the AstraZeneca vaccine in under-55s while officials investigate reports of rare blood clots

Coronavirus vaccine canada
A nurse is inoculated with the Pfizer/BioNTEch coronavirus vaccine in Toronto, Canada, December 14, 2020.

  • Canada paused its AstraZeneca vaccine rollout in people under 55 on Monday.
  • Officials cited reports of a rare blood disorder in young women in Europe.
  • The recommendation was a precaution based on “international data” and a “good supply” of alternative vaccines.
  • See more stories on Insider’s business page.

Canada has temporarily stopped giving AstraZeneca’s COVID-19 vaccine to people under 55 while it investigates cases of an unusual blood-clotting disorder in Europe.

Canadian officials said there were reports from Europe of a clotting disorder among some vaccinated people in Europe, particularly among young women, called Vaccine-Induced Prothrombotic Immune Thrombocytopenia (VIPIT). In this disorder, antibodies “activate” platelets and cause blood clots to form.

“The National Advisory Committee on Immunization (NACI) recommends immediately pausing the use of the AstraZeneca vaccine in all individuals less than 55 years of age in Canada,” NACI said in a statement late on Monday.

This mirrors similar suspensions in Europe: France, for example, has also suspended the shot for younger people.

NACI said the move was a “precaution,” and that it still recommended AstraZeneca’s vaccine for those over 55 years old. This older age group has a higher risk of hospitalization and death from COVID-19, and VIPIT appears to be less common in this group.

Eight of Canada’s 10 provinces, including Ontario, Manitoba, and Quebec, confirmed they had stopped giving AstraZeneca’s vaccine to those under 55 years old following NACI’s announcement.

Several countries in Europe, including France and Sweden, have also suspended AstraZeneca’s shot in younger people, pending an investigation into reports of rare blood clots. Health officials in Berlin, Germany, said Tuesday that the city would stop its rollout in under 55s while investigations were ongoing, DW reported.

Most of the 18 countries that suspended the shot during the European Medicines Agency’s initial investigation into reports of blood clots have restarted vaccinations with AstraZeneca’s vaccine in all age groups.

Read more: COVID-19 Vaccine Tracker: AstraZeneca’s shot proves safe and effective, and is headed to the FDA

NACI said Health Canada was investigating the exact mechanism by which the AstraZeneca could vaccine trigger so-called VIPIT, and that it was not yet clear how common the disorder was.

NACI said that its recommendation was also based on a “good supply” of alternative vaccines from Pfizer-BioNTech and Moderna. Canada was expected to receive enough COVID-19 vaccines to fully vaccinate its population before fall 2021, it said.

So far, less than 2% of Canada’s population are fully vaccinated, according to Johns Hopkins University.

No reports of blood clots in Canada from AstraZeneca shot

Health Canada said that it hadn’t received any reports of blood clots in the country. Dr. Supriya Sharma, Health Canada’s chief medical advisor, told The Guardian that she still believed the vaccine’s benefits outweighed the risks.

NACI acknowledged in the statement that the relatively high number of young women who reported with VIPIT could be related to the vaccine’s rollout – young healthcare workers were one of the early priority groups, and this group includes a high proportion of women. When the shot was first authorized in the EU, Germany, France, and Italy did not give the shot to over 65s, so more younger people could have received AstraZeneca’s shot.

Around 20 million people had received AstraZeneca’s vaccine as of March 16 in the UK and Europe. Seven cases of blood clots in multiple blood vessels and 18 cases of blood clots in the brain had been reported to the European Medicines Agency (EMA).

The EMA investigated these cases and said March 19 that the benefits of AstraZeneca’s shot in preventing COVID-19 – which has killed 2.6 million people worldwide – outweighed the risk of any side effects.

But it couldn’t rule out a link between the vaccine and very rare, serious blood clotting disorders, particularly in women under 55 years old, it said. The EMA is looking into this further, and is expected to announce any further findings next week.

“It’s reasonable to pause for a period of time while this [risk] continues to be evaluated,” Sharma said, per the Wall Street Journal. “I fully understand this can be confusing. Especially for this vaccine, which has had a lot of confusion surrounding it,” she added.

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Vaccines don’t cause blood clots, but younger women have a higher risk of clots in general. Here’s what that means for you.

birth control pill
  • A review of vaccine safety data found blood clots were most common in women under 55.
  • Getting a COVID-19 vaccine will not increase your risk of blood clots.
  • But the birth control pill, pregnancy, and obesity can lead to a higher preexisting risk.
  • See more stories on Insider’s business page.

After a preliminary review of AstraZeneca COVID-19 vaccine data, the European Medicines Agency (EMA) concluded last week that the shot was not associated with an increased risk of blood clots.

The number of clots reported after vaccination was actually lower than expected in the general population, the EMA said in a press briefing Thursday.

But one subset of the vaccinated population experienced more blood clots than normal: women under 55 years old.

Young women are at a higher risk of developing certain types of blood clots regardless of their vaccine status, Mary Cushman, a professor of medicine at the University of Vermont’s Larner College of Medicine, told Insider. Hormonal birth control and pregnancy may play a role in this elevated risk.

Sabine Straus, head of the EMA’s safety committee, said in Thursday’s briefing that an increased risk of clotting due to birth control pills is “always a distinct possibility,” and the EMA may investigate it further in the near future.

Birth control pills and pregnancy both increase the risk of blood clots

Young women are relatively high-risk for blood clots since they’re most likely to take the birth control pill or get pregnant, which both increase the odds of developing a clot, Cushman told Insider.

In fact, the risk of getting a blood clot as a side effect of the pill is much higher than the likelihood of clotting due to the vaccine. Scientists have known about this risk factor for decades, and it recently came up in a TikTok video.

“Millions of women everywhere take the contraceptive pill, and amongst the hundreds of side effects that come with the contraceptive pill – one of which is death – there’s a 6 in 10,000 chance of getting a blood clot,” TikToker alysselizabeth said in the video.

The US Food and Drug Administration estimates that between 3 and 9 out of 10,000 women who take certain birth control pills will develop a blood clot each year, compared to 1 to 5 women per 10,000 who do not have risk factors for blood clots.

Estrogen, a sex hormone that is in most oral contraceptives and spikes during pregnancy, is one reason for that elevated risk, Insider’s Anna Medaris Miller previously reported. The hormone has also been found to affect how immune cells respond to flu vaccines.

There are other risk factors for blood clots – including COVID-19

Obesity and genetic factors can also increase someone’s risk of developing a blood clot, Cushman said. Physical activity and other healthy lifestyle choices can help manage that risk.

“It’s always really important to stay active, avoid sedentary time, keep to a healthy weight, and have a healthy diet,” Cushman said. “And if you’re using an oral contraceptive, or if you have obesity, maybe just ratchet up your awareness a little bit, but don’t avoid the shot.”

She added that COVID-19 has been linked to deadly blood clots, too – so getting vaccinated will help prevent clots by lowering your chance of getting sick from the coronavirus.

“The bottom line is that the risk of adverse health consequences from COVID-19 far outweighs any risk of the shot,” Cushman said.

Read the original article on Business Insider

The US hasn’t authorized AstraZeneca’s vaccine for 2 main reasons. That could change in April.

Veran France vaccination health minister AstraZeneca
French Health Minister Olivier Veran receives the AstraZeneca-Oxford COVID-19 vaccine on February 8, 2021.

  • The US hasn’t authorized AstraZeneca’s vaccine because its trial is still going.
  • Vaccine experts have also questioned inconsistencies in the company’s global studies.
  • AstraZeneca’s US trial results will likely clear up confusion in April.
  • See more stories on Insider’s business page.

After more than a dozen countries paused the use of AstraZeneca’s coronavirus vaccine due to concerns about blood clots, the European Medicines Agency concluded on Thursday that the vaccine doesn’t increase the risk of clotting.

The World Health Organization, too, recommended that countries continue to administer AstraZeneca’s vaccine, since the benefits of the shot “outweigh its risks.”

The US, however, never greenlit the vaccine in the first place, for two main reasons. The first is that AstraZeneca’s US trial is still ongoing. The trial was delayed for nearly seven weeks in the fall due to an adverse reaction in a UK participant.

The second is that AstraZeneca’s initial trial results in November puzzled many experts. The company combined data from its Brazil and UK groups, even though they had different sample sizes and demographics. It also averaged the results of two different dosing regimens, one of which was administered by mistake.

Now, scientists hope that results from AstraZeneca’s US trial will clear up much of the world’s confusion. The findings are expected to be released to the public within the next month.

Currently, the US data is being reviewed by an independent monitoring board. If the vaccine is found to be safe and effective, the FDA could authorize it for emergency use in April, Reuters recently reported.

The US trial has more than 30,000 participants

Even if AstraZeneca’s global trials had been free of inconsistencies, the FDA would most likely still have wanted to see the results of the US trial before authorizing the shot.

The US trial is larger than its predecessors in other countries. The study involves up to 32,000 volunteers – roughly the same number as the clinical trials done by Pfizer and Moderna. And it’s only testing one regimen: two full doses.

“The US study is the one that’s going to be the definitive study to tell us how this vaccine works against severe, hospitalized COVID and symptomatic COVID,” Anna Durbin, a vaccine researcher at Johns Hopkins Bloomberg School of Public Health, told STAT.

AstraZeneca CEO Pascal Soriot
Pascal Soriot, executive director and CEO of AstraZeneca, testifies before the Senate Finance Committee on February 26, 2019.

The trial could also shed light on how the vaccine performs among older people. Nearly one-quarter of the US trial participants were over 65, according to Biopharma Dive. Meanwhile, just 12% of participants in AstraZeneca’s UK and Brazil trials were over 55.

Murky data from the UK and Brazil

The FDA requires coronavirus shots to prevent disease in at least 50% of vaccine recipients.

In November, AstraZeneca reported that its shot was 62% effective at preventing COVID-19 among nearly 9,000 volunteers in Brazil and the UK. Those participants received two full doses, but about 2,700 others accidentally got a half dose followed by a full dose. Among that smaller group, the vaccine’s effectiveness rose to 90%.

AstraZeneca averaged the two results, stating that the vaccine was 70% effective.

“To people looking in from the outside, that doesn’t make a whole lot of sense,” Dr. Johan Bester, director of bioethics at the University of Nevada, Las Vegas School of Medicine, told Insider last month. “We’re either going to give half doses or full doses to people and it will either be one effectiveness or the other.”

AstraZeneca’s shot may be less effective against the variant found in South Africa

In the months since AstraZeneca revealed its global trial results, subsequent analyses have found even more variation in the shot’s effectiveness.

A February analysis that hasn’t been peer reviewed found that the vaccine was 55% effective when doses were given less than six weeks apart, but 82% effective when doses were given at least 12 weeks apart. The results were based on trials in Brazil, South Africa, and the UK with more than 17,000 volunteers in total.

Denmark COVID-19 AstraZeneca
AstraZeneca COVID-19 vaccines in storage in Copenhagen, Denmark on February 11, 2021.

Another study that’s still awaiting peer review indicated that the vaccine was just 22% effective against mild and moderate illness caused by B.1.351, the variant first identified in South Africa. As a result, South Africa halted its distribution of AstraZeneca’s vaccine. But that study was small, with roughly 2,000 participants.

When it comes to two other prominent variants – B.1.1.7, initially spotted in the UK, and P.1, first identified at a Japanese airport among travelers from Brazil – preliminary data shows AstraZeneca’s vaccine has the same efficacy: between 60% and 90%.

The US trial may not give any more clarity about how well the vaccine works against these three variants, since it’s not yet known how many volunteers wound up getting exposed to those strains during the study. But the fact the trial is happening later than Pfizer’s or Moderna’s means there’s a greater chance that participants in this one were exposed to new variants.

Even in the worst-case scenario, Bester said, the shot will probably be effective enough to meet FDA standards.

“What we’ve seen is promising,” he said. “It is a moderately to very effective vaccine that is cheaper than the other alternatives and gives us another tool in our arsenal to stop people from dying.”

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