Bengaluru: The class action lawsuit against global pharmaceutical giant AstraZeneca in the UK and the submission by the drug maker in court earlier this week about the blood clot risk in rare cases from its Covid vaccine has many questioning its safety.
Within the medical community, doctors and researchers are confident that there is no cause for concern. Allergic reactions to vaccines — if any — manifest immediately, within a few minutes after they are administered, while vaccine-induced immune thrombotic thrombocytopenia, or VITT, sets in within 5 to 30 days of vaccination.
The Oxford-AstraZeneca COVID-19 vaccine was manufactured by the Serum Institute in India under the brand name — Covishield.
ThePrint answers some common questions that have cropped up since AstraZeneca’s acknowledgement of the possible side-effect in court.
What are the “very rare” side effects of AstraZeneca’s Covid vaccine?
The identified side effect that AstraZeneca admitted to is called Thrombosis with Thrombocytopenia Syndrome, or TTS. Thrombosis is the production of blood clots in the bloodstream, and thrombocytopenia refers to low platelet levels. TTS can lead to production of blood clots in the body that can travel through the veins or arteries, and can be life threatening, especially if they reach the brain.
Thrombosis is not unheard of. It can happen to people who are otherwise healthy, but are injured, pregnant, have cancer, have had a long surgery, or even those who are on specific oral contraceptives. Liver patients or those with certain autoimmune diseases are susceptible to thrombocytopenia. The combination of the two, however, is not found commonly outside of cancer patients, unrelated to vaccination.
VITT, which is pertinent to the AstraZeneca vaccine was identified in March 2021. It sets in within 5 to 30 days of administration of the vaccine dose and is largely caused because of a genetic mutation called PF4.
How frequently does VITT occur?
Studies on the adverse events from Covid vaccination have indicated high levels of safety and efficacy. A 2021 UK study found 79 cases of VITT in over 20 million vaccinations, while another one the same year showed 28 incidences in 17 million. A 2022 study showed 7.5 VITT cases per million vaccinated people, and a 2024 multi-country study shows seven cases in nearly 99 million individuals across all types of vaccines.
How is VITT caused?
Those with pre-existing thrombocytopenia or thrombosis run the risk of VITT. The exact mechanism of how VITT is caused is unknown and is still being studied. Among those who acquired VITT, studies have indicated that a gene associated with a cytokine (immune system protein) called platelet factor 4 or PF4 contained a mutation. As the name suggests, the PF4 gene plays a role in the body’s ability to produce platelets and clot blood.
How long do side effects from vaccines last?
Allergic reactions manifest immediately, within a few minutes after vaccination. Therefore, people are required to wait in hospitals after taking the jab. Other strong side effects like nausea, headaches, diarrhoea might occur for up to 2 weeks after vaccination, after which they resolve naturally. Incidences of VITT occur for up to 42 days or six weeks from vaccination.
Are there other serious side effects?
Yes, there have also been cases of encephalitis and myocarditis recorded after vaccination. These numbers are just as low or even lower than those of VITT.
What new information do we have?
Nothing. Studies about the safety of vaccines have been conducted since 2021 after they were rolled out. These are often also a part of the vaccine trial itself, as phase 4 of these trials constitutes long-term monitoring of those who have received the vaccine.
How safe is vaccine manufacturing and distribution?
This particular vaccine was developed by Oxford University and first manufactured by AstraZeneca. In India, it is manufactured by the Serum Institute of India. SII is the largest producer of vaccines in the world, and has distributed vaccines to multiple countries through WHO and UNICEF programmes since 1966. Any manufacturer is allowed to and required to produce the formulation developed by the team at Oxford.
How do the vaccines work?
Adenovirus-vector vaccines, such as Covishield, use a weakened adenovirus that is incapable of causing infection (common cold) or dividing. This virus is used to carry a protein into the body; in this case, the coronavirus spike protein alone. The virus will not be able to cause disease, but will still infect the body and enter it.
The immune system can quickly kill a single virion or even a group of viruses, and when it does so, it encounters the spike protein. This is identified as another foreign body to attack, and the vaccine recipient then gets a fever because raising the body temperature is harmful to pathogens. The immune system then trains itself to identify the spike protein, and thus can quickly stave off the actual Covid virus.
mRNA vaccines are brand new and have been administered to humans for the first time. mRNA acts much like a secret letter that gets read and then promptly burned. Instructions in an mRNA are decoded and executed like a computer programme, making the body build an artificial spike protein. The same immune attack process then repeats, and the mRNA is long destroyed before the protein is produced.
Are mRNA vaccines safer? Why did India not buy them?
Statistically, mRNA vaccines are indeed safer, as the mRNA ‘instructions’ make the body produce the foreign spike protein itself, instead of introducing an external spike protein, like Covishield does. However, people could still be allergic to ingredients used in the vaccine.
The mRNA vaccines available today require extremely cold storage because mRNA degrades easily at room temperature. Cold storage is expensive, and mRNA vaccines are mostly used in wealthier countries. Adenovirus-vector vaccines, like Covishield, are comparatively easier to produce, store and transport, and function better for low- and middle-income countries, as well as those in tropical and equatorial regions.
(Edited by Mannat Chugh)
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