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How AstraZeneca's Rare Blood Clotting Side Effect Led to a Global Covid-19 Vaccine Setback

By: Pritha Mallick

Edited By:


Last Updated: April 09, 2021, 15:55 IST

Representative photo

Representative photo

The European Medicines Agency's review of the AstraZeneca vaccine has raised concerns, but health experts worldwide have said the benefits of the AstraZeneca jabs far outweigh the risks.

The European Medicines Agency in its recent probe noted that there is a possible link between the AstraZeneca coronavirus vaccine and a rare blood clotting disorder. While the EU body did not place any new restrictions on using the vaccine on people of 18 years of age and over, the widely reported review has raised concerns among the tens of millions who have received at least one dose of the shot.

Cheaper and more easily stored than other Covid-19 vaccines, and hailed to be safe and 79% effective at preventing symptomatic Covid-19, the vaccine has been suspended in people under 60 years of age in many countries including South Korea and the Philippines.

Rare Blood Clots

Known as cerebral venous sinus thrombosis (CVST), it is a very rare and specific type of blood clot in the brain occurring together with low levels of platelets (thrombocytopenia) following vaccination. Noting the condition as “unusual", the French Medicines Agency (ANSM) told AFP, “This thrombosis of large veins is unusually located in the brain, and even more rarely in the digestive tract."


Germany’s medical regulator Paul Ehrlich Institute (PEI) was one of the first to flag this condition in mid-March among an abnormally high number of cases mostly in younger and middle-aged women. Germany halted the use of the vaccine for people under 60. Several nations, including Canada, France and Spain, and Italy recommended minimum age for recipients after similar reports.

Australia recommended people under 50 should get Pfizer’s Covid-19 vaccine in preference to AstraZeneca’s. The Netherlands temporarily suspended the use of the AstraZeneca shots for people under 60 following the death of a woman who had received a shot last week, the Health Ministry said. About 10,000 scheduled appointments for vaccinations were to be scrapped as a result of the decision, news agency ANP reported.

Europe recorded 222 cases of a rare thrombosis affecting the brain or abdomen among its 34 million people who had received the AstraZeneca vaccine till April 4. The condition had already led to 18 deaths as of March 22.

In the UK, the vaccine advisory committee released a statement soon after the EU’s ‘possible link’ remark that an alternative to the Oxford-AstraZeneca’s vaccine should be given to people under 30, where possible. A day before, Oxford University paused administering doses of its Covid-19 vaccine it developed with AstraZeneca for a small UK study in children and teenagers.

‘Outdated Information’

The US National Institute of Allergy and Infectious Diseases (NIAID) in a statement released on March 23 said AstraZeneca “may have included outdated information” in its initial data of Covid-19 vaccine trials in America. The observation came just a day after the drugmaker announced that its shot was 79% effective at preventing symptomatic Covid-19 and 100% effective against severe illness and hospitalisation. A hurried review by the company’s team showed that overall efficacy dropped 3 percentage points, to 76%, though it actually rose 5 percentage points in seniors, to 85%. The vaccine was announced 100% effective at preventing hospitalization and severe disease.

Indian Context

The Union Health Ministry is reviewing all “serious and severe” adverse event reported during the vaccination drive, Dr NK Arora, Head Operations Research Group of National Covid-19 Task Force told the BusinessLine. “The report will likely be released by the health ministry this week," said Arora who is also the advisor to the national AEFI committee. The national AEFI ( adverse events following immunisation) cases will also be updated to include instances reported till the end of March. India had reported 234 AEFIs, including 71 deaths till March 12.

Manufactured in India by the Serum Institute of India (SII), the Oxford-AstraZeneca vaccine is one of the two vaccines being used in its national vaccination drive, the other being Covaxin made by the domestic company Bharat Biotech. The SII-AstraZeneca partnership agreed to produce more than 1 billion doses for low and middle-income countries.

The African Union dropped its plans to buy AstraZeneca’s vaccine from SII and is exploring options with Johnson & Johnson the head of the Africa Centres for Disease Control and Prevention said.

The WHO on Thursday rejected SII’s proposal seeking extension of the shelf life of Oxford-AstraZeneca Covid-19 vaccine, Covishield, from six to nine months, citing insufficient data, reports PTI. The move comes even as drug regulator, Drugs Controller General of India (DCGI), has extended Covishield’s shelf life from six to nine months from its manufacturing date.

The Indian vaccine maker is currently facing a lawsuit by AstraZeneca over vaccine supply delays. “AstraZeneca has sent us a legal notice (for delays in supplying the vaccine) and the Indian government is also aware of that. I cannot comment on the legal notice as it is confidential, but we are examining all avenues to amicably manage and resolve legal disputes over contractual obligations that Serum Institute is not able to fulfil due to its prioritisation of Indian supplies," SII CEO Adar Poonawalla told the Business Standard.

Indonesia who is slated to receive 54 million doses of the AstraZeneca vaccine from India in phases via the COVAX global-vaccine alliance scheme, said it is in talks with China’s Sinovac Biotech on getting as many as 100 million Covid-19 vaccine due to delay in SII’s vaccine exports.

The delay comes as several states, including India’s worst covid-19-hit state, Maharashtra, raised alarm over vaccines shortages. Union Health Minister Harsh Vardhan on Thursday dismissed the concerns as a “hue and cry" to curtail states’ inefficiency to contain the virus spread. In a statement, he said that 9.1 crore vaccine doses have been utilised, while 2.4 crore are in stock and 1.9 crore vaccines are in the pipeline, indicating sufficient doses available for all states.

Where do we stand now

Someone getting the AstraZeneca vaccine stands a 1-in-153,000 chance of cerebral venous sinus thrombosis (CVST), AFP reported citing recent data.

Meanwhile, the US chief medical adviser to President Joe Biden, Dr Anthony Fauci said the US does not need AstraZeneca’s doses. “We have three excellent vaccines. Even if the FDA deems that this vaccine is a very good vaccine, we don’t need yet again another very good vaccine. We have enough very good vaccines," he told CNN.

The UK began the Moderna Covid vaccine rollout, the third two-dose vaccine now being administered by the National Health Service (NHS) alongside the Pfizer-BioNTech and Oxford-AstraZeneca jabs.

In India, Russia’s Sputnik V vaccine will likely receive authorisation “very soon", top government sources told CNN-News18. The addition will help India reduce its current logistical burden.

Health experts worldwide, including the WHO, have reiterated that the benefits of the AstraZeneca jabs far outweigh the risks, that the vaccine is safe, and has saved thousands from the Covid-19 infection that has claimed over three million lives since the outbreak began more than a year ago.

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first published:April 09, 2021, 10:55 IST
last updated:April 09, 2021, 15:55 IST