How it works
COVID-19 Vaccine AstraZeneca is a vaccine for preventing coronavirus disease 2019 (COVID-19) in people aged 18 years and older. COVID-19 is caused by SARS-CoV-2 virus. COVID-19 Vaccine AstraZeneca is made up of another virus (of the adenovirus family) that has been modified to contain the gene for making a protein from SARS-CoV-2. COVID-19 Vaccine AstraZeneca does not contain the virus itself and cannot cause COVID-19.
Once injected, it teaches the body's immune system how to fight the real virus, should it need to.
Unlike Pfizer's vaccine, which has to be kept at an extremely cold temperature (-70C), the Oxford vaccine can be stored in a normal fridge. This makes it much easier to distribute.
Approved for use
The vaccine has been approved for use in the United Kingdom and several European Union countries since December 2020. It has not yet been approved in the U.S. because the Food and Drug Administration (FDA) asked the company to provide results from a large-scale trial, the Vox reported.
The US 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 2020 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.
Cases of blood clots
The United Kingdom, European Union, and Scandinavian countries have reported that the AstraZeneca COVID-19 vaccine appears to be associated with rare cases of serious blood clots, including blood clots in the brain. These blood clots have two important features: they occur 4 to 20 days after vaccination, and they are associated with low platelets (tiny blood cells that help form blood clots to stop bleeding). Doctors are calling this “vaccine-induced prothrombotic immune thrombocytopenia” (VIPIT). VIPIT seems to be rare, occurring in anywhere from 1 in every 125,000 to 1 in 1 million people.
A cascading number of European countries – including Germany, France, Italy and Spain – suspended use of AstraZeneca’s COVID-19 vaccine on March 15, 2021 over reports of dangerous blood clots in some recipients, though the company and international regulators say there is no evidence the shot is to blame.
Germany’s health minister said the decision to suspend AstraZeneca shots was taken on the advice of the country’s vaccine regulator, the Paul Ehrlich Institute, which called for further investigation into seven cases of clots in the brains of people who had been vaccinated.
French President Emmanuel Macron said his country will likewise stop dispensing the vaccine until at least Tuesday afternoon (March 16). Italy also announced a temporary ban, as did Spain, Portugal and Slovenia.
Other countries that have done so over the past few days include Denmark, which was the first, as well as Ireland, Thailand, the Netherlands, Norway, Iceland, Congo and Bulgaria.
The northern Italian region of Piedmont on Sunday (March 14) said it had blocked use of the vaccine as investigations were carried out after the death of a teacher who had received it the day before.
The woman, who age has not been disclosed, died on Sunday in the town of Biella, north of Turin.
On Sunday, health ministry inspectors arrived in Sicily in the south of the country to investigate the death there of a 43-year-old soldier last Tuesday (March 9) after having received the vaccine.
“This is an extreme precautionary measure, while waiting to see if a causal link exists between the vaccination and the death,” said a statement from regional health advisor Luigi Genesio Icardi.
On March 18, the European Medicines Agency (EMA) completed its review of the AstraZeneca vaccine, which is made in partnership with Oxford University, and concluded that it is safe and effective, BBC News reports. The E.U.’s medical regulation agency had revisited the vaccine’s safety because, out of about 17 million people who had gotten the shot by early March, 37 people developed unusual blood clots.
On March 22, AstraZeneca released its initial results of the Phase III trial, which showed slightly higher effectiveness at preventing Covid-19 than the latest results. The results were long-awaited. The FDA asked the company to conduct a larger trial in order to get clearer data than they gathered in their first rounds of testing. In the first trials in the U.K., some participants unexpectedly received half-doses of the first shot in the vaccine, and the early trials did not include enough people older than 65, the Washington Post reported.
By the morning of March 23, officials at the National Institute of Allergy and Infectious Diseases released a letter from its data and safety monitoring board that's been examining the AstraZeneca trial, the STAT News reported. The letter stated that AstraZeneca had used outdated data to reach its efficacy number. The move was unprecedented; usually, monitoring boards keep their correspondence with companies private.
“We just felt we could not remain silent. Because if we did remain silent, we could be understandably accused of covering something up. And we definitely didn’t want to be in that position,” says Anthony Fauci, director of the NIAID, to STAT News. “In my mind, it’s an unforced error by the company.”
AstraZeneca explained the initial results included data gathered until February 17, per Nature.
Within 48 hours, AstraZeneca released its revised results with updated data. According to the statement, the vaccine has 76 percent efficacy at reducing symptomatic Covid-19 overall, and 85 percent efficacy in people 65 years old and older. A specific review of the 32,000 participants in the U.S. trial found no cases of the unusual blood clots that caused hesitation in Europe, per STAT News.
Seven people have died from unusual blood clots after getting the Oxford-AstraZeneca vaccine in the UK, the medicines regulator has confirmed to the BBC.
In total, 30 people out of 18 million vaccinated by March 24 had these clots.
It included 22 reports of cerebral venous sinus thrombosis, an extremely rare brain ailment, and eight reports of other clotting events associated with low blood platelets soon after getting the controversial jab.
As of March 30, three deaths in people who experienced a combination of blood clotting, low platelet count and hemorrhaging three to 14 days after receiving the vaccine were reported in Norway, the country's medicines agency said in a report. Norway has administered at least one dose of the AstraZeneca to more than 134,000 people.
"The Norwegian Medicines Agency believes that there is a probable link with the vaccine, but we need more research to clarify exactly what is triggering this," it wrote.
Denmark reported two cases of blood clots and low blood platelet counts after the vaccine; one of the cases was fatal.
Germany’s vaccine regulator said on Tuesday (March 30) it has recorded 31 cases of a rare blood clot in the brain, nine of which resulted in deaths, after people received a COVID-19 vaccine from AstraZeneca.
The Paul Ehrlich Institute (PEI) said it has now registered 31 cases of clots in the cerebral veins – known as sinus vein thrombosis, or CSVT – and that in 19 of these there was a deficiency of blood platelets or thrombocytepenia.
In nine cases, the affected people died. With the exception of two cases, all reports concerned women between the ages of 20 and 63. The two men were 36 and 57 years old.
A statement from Dr. Andreas Greinacher, March 31
Dr. Andreas Greinacher led the team that discovered the link between the AstraZeneca vaccine and a rare blood clotting disorder, but he wants people to know the risk of developing the clots is low.
Dr. Greinacher is Head of the Institute of Immunology and Transfusion Medicine, University Hospital Greifswald, Germany.
Greinacher found that in some patients, the AstraZeneca vaccine was triggering antibodies that set off a platelet response. That means the the antibodies made the platelets, small blood cells that help form clots to stop bleeding, behave as though they were treating a wound and trigger clotting.
At a press conference on Wednesday (March 31, 2021), Greinacher said that the causal link is still unknown, and there could be co-factors in the small number of patients who developed vaccine-induced prothrombotic immune thrombocytopenia (VIPIT). VIPIT is the name given to the type of clotting that seems to occur as a rare reaction to the AstraZeneca vaccine.
“It could very well be that in these individual patients are two or three co-factors present at the same time, which together at the time point of vaccination trigger these antibodies,” he said.
While his team continues to investigate what exactly causes this reaction, Greinacher said that there are far fewer people developing this antibody response than are getting sick with COVID-19.
“The number of individuals being severely sickened by the pandemic, by COVID-19, outnumber those who suffer from the vaccination reaction by several orders of magnitude,” he said.
Within the span of two weeks, Greinacher and his colleagues were able to develop a screening test, a test to confirm the response in a lab and now, a potential treatment.
“The first anecdotal feedbacks I receive from treating physician, it seems to work quite well,” he said.
The focus now for Greinacher and his colleagues is determining how the vaccine is associated with, or induces, this response in the body.
“I have to say very clearly, there is no direct link that the vaccine itself is inducing the antibody, it could be that the vaccine is triggering something else in the human body, which then is modifying the immune system, which is then starting to produce the antibodies,” he said.
“It's too early to make a really clear correlation and very clear association between the vaccine and formation of the antibodies,” he added.
His message is clear: While there is a risk of having an adverse reaction to the AstraZeneca vaccine, the risk is so small that people shouldn’t be concerned about getting the vaccine.
“To stop or to avoid vaccination, only for the fear of getting an extremely rare, adverse reaction would be completely wrong.”
Some countries are restricting the use of the AstraZeneca vaccine against COVID-19 while others have pressed ahead with inoculations as investigations into reports of rare, and sometimes severe, blood clots continue.
The European Union’s medicines regulator – the European Medicines Agency (EMA) – and the World Health Organization (WHO) have said the benefits of the shot outweigh its potential risks, but they are monitoring the situation as more cases are reported.
On March 31, EMA chief Emer Cooke said there was “no evidence” yet that would support restricting the use of AstraZeneca’s vaccine in any population despite the reports of rare blood clots.
Her comments came after an independent vaccine expert panel in Germany said a day earlier that the AstraZeneca shot should not routinely be given to people under the age of 60 because of a rise in reported cases of unusual blood clots in the days after vaccination.
The German government followed the recommendation and said the shot would be limited for use in people aged 60 and above.
As of March 31 the vaccine is being used by the following countries
The Therapeutic Goods Administration said on March 31 that a link between the vaccine and clot disorders had not been proven but that it was still investigating the issue as vaccinations continue.
Resumed inoculations from March 19.
Canada continued to use the vaccine, albeit with limits, having paused offering the shot to people aged under 55 on March 29.
Cyprus, which suspended the vaccine on March 15, resumed inoculations on March 19.
The country’s medical regulator approved the resumed use of AstraZeneca’s vaccine on March 19, but said it should only be given to people aged 55 and older.
Resumed using the AstraZeneca vaccine from March 29, but will only give it to people aged 65 and over.
Has limited the use of the vaccine after a nurse died of anaphylactic shock, and vaccinations will continue only in full-fledged medical centres, news agency TASS reported on March 19.
Germany limited use of the shot to people over 60 years of age and high-priority groups from March 31, following further reports of a rare brain blood disorder.
Resumed use on March 25 after suspending it on March 11 pending investigations into reports that it might be linked to blood clots.
Resumed using the vaccine on March 22 but warned against the use of the vaccine in people with a low blood platelet count.
Resume roll-out of the vaccine for all those aged 18 and over on March 20, after suspending it on March 14.
Resumed using the vaccine on March 19, and Italians who decline to be inoculated with it will be given an alternative later on.
Also said it would restart administering the shots from March 19.
Restarted administering the vaccine on March 19, currently for people over age 65 only.
The health minister said on March 18 that the country would resume using the vaccine that week.
Health Minister Venko Filipce said on March 31 that AstraZeneca shots would be limited to people aged over 60 as a precautionary measure.
President Moon Jae-in received the vaccine on March 23 ahead of an overseas trip, as the country inoculates senior citizens and health workers.
Spain said on March 30 that it would use the vaccine for people aged 55-65, and a day later said it would extend the vaccination to essential workers over 65 years old.
Resumed use of the vaccine on March 25 for people aged 65 and older, its health agency said, but restrictions are in place for Swedes under 65 years old.
Began use on March 15, with Prime Minister Prayuth Chan-ocha becoming the first to be inoculated, after Thailand delayed rollout the week before.
As of March 31 the following countries suspended use of the vaccine
Suspended use of one batch of the vaccine on March 7 after the death of one person and the illness of another.
Suspended administration of the vaccine it was scheduled to receive on March 20 as part of the COVID-19 Vaccines Global Access Facility (COVAX) sharing scheme, the health ministry said.
Prolonged its suspension of the shot by three weeks pending further investigations after its two-week pause ended on March 25. A local survey indicated that one in three Danes would decline to get the shot.
Norway will delay a decision over the use of the vaccine, authorities said on March 26, with a decision expected by April 15.
Temporarily stopped vaccinating people with one batch of the vaccine on March 11.
The Netherlands is the latest country to restrict the rollout of the Oxford-AstraZeneca jab, after saying on Friday (April 2) that it was suspending its use for people under the age of 60.
The Dutch health ministry said the precautionary measure was taken after five reports of blood clots in combination with low platelet counts in women between the ages of 25 and 65.
All appointments for those under-60s scheduled to receive the jab have been cancelled with immediate effect. The suspension will remain in place until April 7 when the EMA is expected to issue new guidance.
Earlier this week, Germany said it was suspending routine use of the jab for people below the age of 60 due to fears over a link with blood clots.
The Netherlands and Germany were among several European countries which briefly suspended use of the jab last month pending an EMA review into the possible link to blood clots.
When the EMA declared the vaccine "safe and effective", they resumed its use while investigations continued.
France already limits use of AstraZeneca to those aged over 55 and on Monday (March 29), Canada recommended immediately suspending use of the jab in people aged below 55 following reports in Europe.
According to an April 6, 2021 Reuters news article: “In my opinion, we can now say it, it is clear that there is an association (of the brain blood clots) with the vaccine. However, we still do not know what causes this reaction,” Marco Cavaleri, chair of the vaccine evaulation team at the European Medicines Agency (EMA), told Italian daily Il Messagero.
Cavaleri provided no evidence to support his comment.
However, the EMA later said in a statement that its review of the vaccine was ongoing and it expected to announce its findings on Wednesday (April 7) or Thursday (April 8). An AstraZeneca spokesman declined to comment on the matter.
The first confirmed case of a rare but potentially fatal blood clot has been recorded in Canada in connection with the AstraZeneca-Oxford COVID-19 vaccine.
Quebec's Ministry of Health and Social Services confirmed a person in the province experienced an adverse event known as vaccine-induced prothrombotic immune thrombocytopenia (VIPIT).
The ministry didn't confirm the age or gender of the person, but Quebec Health Minister Christian Dubé later identified the individual as a woman.
"The good news is, the woman in question was taken care of and she's doing well," he said during a news conference Tuesday (April 13).
The National Advisory Committee on Immunization (NACI) said last month VIPIT occurs at a rate of about one in 100,000 people vaccinated, with a mortality rate of about 40 per cent, although more research is needed and that risk is reduced if treated early enough.
Dubé said the province is taking a "hypervigilant" approach and keeping a close eye on any adverse reactions related to the vaccine. He said this was a possibility that health officials "expected" and prepared for.
"We have been very transparent that there could be one case per 100,000," he said. "We knew this could happen."
Denmark has become the first country to permanently halt the use of AstraZeneca’s COVID-19 vaccine following its possible link to very rare cases of blood clots.
The Danish health authority said on Wednesday (April 14) that, following its own review, the country’s vaccine rollout would continue without the AstraZeneca shot, as it warned of a “real risk of severe side effects.”
“Based on the scientific findings, our overall assessment is there is a real risk of severe side effects associated with using the COVID-19 vaccine from AstraZeneca,” said DHA director general Søren Brostrøm. “We have, therefore, decided to remove the vaccine from our vaccination program,” he added.
The health agency said it agreed with the European Union drug regulator’s assessment that the benefits of the vaccine outweigh the risks, but noted that the watchdog urged individual countries to consider their own situations and vaccine availability when making a judgment.
Brostrøm said the epidemic was currently under control in Denmark, with a large proportion of the older population vaccinated and those yet to be inoculated at less of a risk.
“We must weigh this against the fact that we now have a known risk of severe adverse effects from vaccination with AstraZeneca, even if the risk in absolute terms is slight,” he added.
Those who have already received the first dose of AstraZeneca will be invited to have a different vaccine second time around, the health authority said.
It added that Denmark could reintroduce use of the U.K.-Swedish drug company’s vaccine at a later date if the country’s situation changes.
Alberta has confirmed Canada’s second rare blood clot case in a patient who received the Oxford-AstraZeneca vaccine, the province’s chief medical health officer announced Saturday (April 17).
Dr. Deena Hinshaw said the male patient, who is in his 60s and recovering, marks the second Canadian case of the blood clot disorder known as vaccine-induced immune thrombotic thrombocytopenia, or VITT.
The diagnosis does not change the province’s risk assessment of the vaccine, she said, adding that she is taking the event “extremely seriously.”
“These blood clots remain extremely rare, and anyone who is aged 55 and older faces much higher risks from COVID-19 infection than from this vaccine,” Hinshaw told reporters on a conference call.
“When it’s quickly identified, appropriate treatment can be put in place to make sure that those who do have this very rare side effect are treated appropriately and then can recover.”
She continued to recommend AstraZeneca for anyone 55 and older, saying it is the best way to protect their health.
New Brunswick reported its first case of blood-clotting in a person who received the Oxford-AstraZeneca COVID-19 vaccine on April 20.
Dr. Jennifer Russell, the province's chief medical officer of health, said the person is in their 30s and received the vaccine in mid-March, before the National Advisory Committee on Immunization (NACI) recommendation on March 29 to not give it to anyone younger than 55.
The person suffered the adverse reaction in the expected range of five to 21 days after getting the shot.
"This person was treated and has recovered," Russell said.
This is Canada's third reported case of the rare blood-clotting reaction to this type of vaccine. It is associated with low platelets and is known as vaccine-induced immune thrombotic thrombocytopenia (VITT).
Ontario has confirmed its first case of rare blood clotting linked to the AstraZeneca COVID-19 vaccine on April 23.
According to provincial health officials, the man in his 60s is currently recovering at home after receiving his first dose of the vaccine. No further details were provided, citing patient privacy.
This is the fourth reported case in Canada of the rare blood-clotting reaction, which is associated with low platelets and is known as vaccine-induced immune thrombotic thrombocytopenia (VITT).
A second case of blood clotting linked to the AstraZeneca COVID-19 vaccine has been confirmed in Ontario on April 23, health officials said. This is the fifth reported case in Canada.
A man in his 60s from Hamilton is receiving care in hospital after he developed rare blood clotting, known as vaccine-induced immune thrombotic thrombocytopenia, following his first dose of the AstraZeneca vaccine, Hamilton Public Health said Friday evening.
This case comes just hours after Chief Medical Officer of Health Dr. David Williams said another Ontario man in his 60s is recovering at home after suffering the same issue.
Quebec has confirmed the death of a woman after the AstraZeneca-Oxford COVID-19 vaccine she received in early April led to a rare blood clot in her brain.
The province's Ministry of Health said the woman's death was caused by a vaccine-induced immune thrombotic thrombocytopenia (VITT).
She has been identified by her family as 54-year-old Francine Boyer.
According to a news release sent out Tuesday (April 27) evening, Boyer and her husband Alain Serres both took the AstraZeneca vaccine on April 9.
While he experienced no complications, she was hospitalized and later died on April 23.
The release states that in the days following her vaccination, Boyer suffered from severe fatigue and headaches. She was hospitalized locally and then transferred to the Montreal Neurological Institute as her condition worsened.
This is the first reported AstraZeneca vaccine-related death in Canada.
Britain’s medicine regulator on Thursday (April 29) said there had been a further 41 reports of rare blood clots after doses of AstraZeneca’s COVID-19 vaccine, but that the benefits of the shot continued to outweigh the risks for the majority of people.
In a weekly update on side effects from COVID-19 vaccines, the Medicines and Healthcare products Regulatory Agency (MHRA) said there were a total of 209 clots with low platelet counts following vaccination with AstraZeneca's shot, compared to a total of 168 reported last week.
There were 41 deaths following the clots in Britain, the MHRA said, an increase of 9 from last week’s figures, although experts say historic cases might still be feeding through to the totals, and the clots are set to remain a rare event.
About 22 million first doses of the AstraZeneca vaccine have been administered in Britain. Four cases of rare clotting were reported following a second dose, but the MHRA did not say how many second doses had been given.
Quebec health officials reported a third case of a rare blood clot linked to Oxford-AstraZeneca’s COVID-19 vaccine on Saturday (May 1).
The Health Department said the unidentified person remains hospitalized but is in stable condition.
The first Albertan to die from a rare blood clot condition linked to a COVID-19 vaccine was turned away from an Edmonton hospital two days before her death, a family friend says.
It is Canada’s second known AstraZeneca vaccine-related death.
Lisa Stonehouse, 52, died Saturday at the University of Alberta Hospital.
Dr. Deena Hinshaw, Alberta's chief medical officer of health, said Tuesday (May 5) that a woman in her 50s died of vaccine-induced immune thrombotic thrombocytopenia (VITT) after receiving the AstraZeneca vaccine.
Hinshaw did not identify the woman, but family members confirm that Stonehouse was Alberta's first fatal case.
Wilfred Lowenberg, a friend, said Stonehouse was turned away from the emergency department at the Grey Nuns Community Hospital. Two days later, she was admitted to the Strathcona Community Hospital. She was later transferred to the U of A Hospital with a blood clot in her brain.
Stonehouse got her shot on April 21. Almost immediately, she felt stiff and sick, Lowenberg said. She felt increasingly unwell and developed an unbearable headache.
On April 29, with her symptoms worsening, she called Health Link but was told she was likely dealing with a normal vaccine reaction, Lowenberg said.
Later that night, her daughter drove her to the ER at the Grey Nuns Community Hospital in southeast Edmonton, Lowenberg said.
Her head was throbbing, and she was weak and vomiting. Stonehouse was sent home to rest, Lowenberg said.
On April 30, her daughter again drove her to the ER, this time at the Strathcona Community Hospital in Sherwood Park. She was admitted. A CT scan showed a blood clot had formed, triggering a fatal bleed in her brain.
Stonehouse was transferred to the U of A Hospital, but in the ambulance she suffered a seizure and was intubated, Lowenberg said.
The following day, she was taken off life support.
An internal investigation is ongoing, Covenant Health said in a statement Wednesday (May 6).
A New Brunswick resident has died after developing blood clots following vaccination with the AstraZeneca vaccine.
The resident, who was in their 60s, is the first person to die in the province from a vaccine-related cause, and this was the second serious case of adverse effects from the vaccine, Dr. Jennifer Russell said Wednesday (May 5).
The person received the AstraZeneca vaccine in mid-April and developed symptoms seven days later. They went to an emergency room for treatment and died two days later in hospital.
Russell would not disclose any other details about the New Brunswick case, including the person's sex or health zone.
This is the third death in Canada linked to the AstraZeneca vaccine.
British Columbia has recorded its first case of a vaccine-induced thrombosis related to the AstraZeneca-Oxford vaccine, a rare side effect of what health officials maintain is still a highly effective vaccine.
Provincial Health Officer Dr. Bonnie Henry and Health Minister Adrian Dix made the announcement at a news conference in the Fraser Health region on Thursday (May 6).
Henry said the affected woman, who was in her 40s and in the Vancouver Coastal Health region, is now stable, emphasizing the condition is extremely rare and can be treated. She said the woman noticed her symptoms five or six days after receiving a dose of AstraZeneca and went to her doctor, who, suspecting it might be a condition related to the vaccine, conducted a diagnostic blood test that revealed low platelet counts.
The Canadian provinces of Alberta and Ontario said on Tuesday (May 11) they would stop offering first doses of AstraZeneca's COVID-19 vaccine, with Ontario citing evidence that the risk of rare blood clots is somewhat higher than previously estimated.
Alberta said it took the same step only because it was unclear when more shipments of the vaccine might arrive, and not due to concern about side effects.
Officials in Ontario said roughly one in 60,000 people who received the vaccine in the province, eight in total, developed the complication, which involves blood clots accompanied by a low level of platelets, cells in the blood that help it to clot.
After distributing more than 2.3 million AstraZeneca vaccine doses nationwide in Canada, public health officials have so far identified 28 suspected cases of a rare but serious condition called vaccine-induced thrombotic thrombocytopenia (VITT).
Dr. Howard Njoo, Canada's deputy chief public health officer, said Thursday (May 13) that 18 of those cases have been verified through testing while 10 more await laboratory confirmation.
There have been four VITT-related deaths reported in Canada.
The report on VITT cases comes after some provinces have suspended the use of the AstraZeneca shot. Alberta, New Brunswick, Nova Scotia, Ontario, Saskatchewan and Quebec have all said they will stop using the vaccine for first doses, at least for now.
In announcing its suspension, Ontario said it now believes the VITT incident rate is roughly 1 in 60,000 shots administered — a rate that is much higher than the figure previously cited by Health Canada.
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