AstraZeneca admits Covishield has rare side effect: Is concern warranted?

AstraZeneca's acknowledgment that the vaccine may lead to thrombosis isn't a new revelation, but it underscores the need for transparent communication by the pharma companies, say experts

UK-headquartered pharmaceutical giant AstraZeneca has admitted that in “very rare cases”, its Covid-19 vaccine can cause low platelet count and a blood clot-related side effect – Thrombosis Thrombocytopenia Syndrome (TTS), according to court papers being quoted in the media.

The Oxford-AstraZeneca’s Covid vaccine is sold as Covishield in India and Vaxzevria in Europe and some other countries. Manufactured and marketed in India in partnership with Pune-based Serum Institute of India, it was widely used during the country’s fight against the deadly Covid-19 pandemic.

Over 1.7 billion doses of Covishield have been administered so far. Given that the world is still recovering from the wounds of the coronavirus crisis, the revelation warrants a careful assessment to avoid any unwarranted public paranoia. Business Standard spoke with doctors about the vaccine controversy to determine if there is a cause for worry.

Rare side-effect

Dr Chandrakant Lahariya, senior consultant physician, vaccines specialist and epidemiologist at Sukhmani Hospital, New Delhi said, “TTS is one of the rare but very serious adverse effects that has happened as part of Vaccine-induced Immune Thrombotic Thrombocytopenic Purpura (VITTP). The linkage between the AstraZeneca vaccine and vaccine-induced immune TTS was scientifically identified in early 2021, soon after the first Covid vaccines had come out. It is important to remember that there is no clinically validated data to showcase young people who died of cardiac events due to Covid-19 vaccinations. The incidences of TTS have been as low as one in a million doses.”

Dr Lahariya, who has spent nearly 15 years with the World Health Organization (WHO), further said, “We need to balance these concerns. Every vaccine has some or the other side effect and there are still many unknowns in the health sector. So, please remember, that although there are extremely rare serious side effects for vaccines, the benefits far outweigh the risks. The number of lives it has saved is much higher. It helped us beat the pandemic.”

Communication imperative

Dr Pavitra Mohan, paediatrician, public health expert, and co-founder of Basic Healthcare Services said, “Astra Zeneca’s admission does underscore the need for transparent communication by the pharmaceuticals and vaccine developers. There is no need to worry based on this information. The side effects are rare and were seen only in young people and only within 4 to 6 weeks of the first dose of vaccination. So, there is no need for panic.”

Speaking to Business Standard, former national president of the Indian Medical Association (IMA) Dr Ravi Wankedekar said TTS is a very rare condition resulting from an abnormal immune response. “While it has several causes, it has also been linked with adenovirus vector vaccines. The WHO has deemed the vaccine safe and effective for all individuals aged 18 and above.”

He added that we are yet to fully understand the impact of coronavirus on people, also called long Covid. “The difficulty is to distinguish between the complications that are caused by Covid itself or the vaccine. That remains debatable. People who are vaccinated have an overall lower risk of complications such as post-Covid heart attacks and strokes among others.”

Dr Wankedekar asserted that the TTS symptoms, which include headaches, blurred vision, chest pain, leg swelling, or tiny blood spots under the skin, manifest between 1-6 weeks of vaccination. “Considering that most Indians received their Covishield jab a couple of years ago, there should be no reason to panic now,” he said.

Why is the clot formed?

Explaining the reason behind the rare outcome of blood clotting after taking the adenovirus vaccines, Dr Rajeev Jayadevan, Co-Chairman, IMA Covid-19 task force said, "Like many things in medicine, the exact mechanism for this is also unknown. It is an unusual immune reaction to a particular vaccine genre which is called as adenovirus vector vaccine. Adenovirus vectors are not disease-causing viruses but these are artificially fitted with the spike of the virus that our immune system needs to fight. In the case of AstraZeneca's adenovirus vector vaccine, a chimpanzee adenovirus - ChAdOx1 - has been modified to enable it to carry the Covid-19 (SARS-CoV-2) spike protein injected into the muscles of humans."

He explained that there are many variables associated with the vaccination process ranging from age, type of vaccine, technique of injection, individual variation in immune response, genetic, HLA-based and hormonal differences, among others. This is why the same vaccine may produce different outcomes in the receivers. In rare cases, the body generates antibodies against its own platelets which then triggers a cascade of events. This and other processes lead to low platelet count and abnormal clotting that occurs in unusual locations where clots commonly do not occur. This condition is called TTS, which also has other causes besides vaccination.

Watch: Covishield can cause blood clots, low platelet count. Here's all you should know