Covishield COVID-19 Vaccine by Oxford-AstraZeneca: Recognized Adverse Reactions
The Oxford-AstraZeneca COVID-19 vaccine, known as Vaxzevria, has been authorized for use in 83 countries, but concerns about rare adverse events continue to be closely monitored.
Recent data confirm that while these incidents, known as vaccine-induced immune thrombocytopenia and thrombosis (VITT), or thrombotic thrombocytopenia syndrome (TTS), are serious, they are extremely uncommon. Studies from Italy and other countries report that thrombotic events following vaccination occur rarely, with most patients recovering.
VITT predominantly involves unusual blood clots accompanied by low platelet counts and is associated with adenovirus vector vaccines like Vaxzevria and Janssen's vaccine. The incidence is about 1 case per 100,000 vaccinations.
The MHRA in the UK has reported 79 cases of blood clotting with low platelet levels, all occurring after the first dose. There have been reports of severe cases of blood clots following Vaxzevria administration in Europe and the UK.
The regulatory agencies suggest that these combined incidents may be a type of immune response. However, the EMA cannot yet conclusively determine whether Vaxzevria directly causes TTS.
The vaccine, which targets the SARS-CoV-2 virus by containing the gene that encodes for the spike protein on the surface of the virus, has a 76% efficacy rate after both doses, according to AstraZeneca's primary analysis of phase 3 trial data.
Common side effects of Vaxzevria include headache, fatigue, muscle or joint pain, fever, chills, nausea, and pain and irritation at the site of the vaccine injection. An allergic reaction to certain ingredients in the vaccine may occur, with symptoms including hives, a rash, swelling, and respiratory symptoms.
The EMA has recommended adding a warning to Vaxzevria's label about the potential risk of Guillain-Barré syndrome, a neurological disorder characterized by the immune system attacking the myelin sheath. However, the EMA cannot yet conclusively determine whether Vaxzevria directly causes Guillain-Barré syndrome.
Individuals may also experience symptoms related to thromboembolic events, such as shortness of breath, chest pain, leg swelling, abdominal pain, neurological symptoms, and tiny blood spots beneath the skin beyond the vaccine injection site. It is important to seek immediate medical attention if any of these symptoms occur.
The vaccine does not contain the SARS-CoV-2 virus itself and does not cause COVID-19. Continuous pharmacovigilance and epidemiological surveillance are ongoing, as reported in 2025 research articles.
In summary, the status of these rare clotting incidents is that they remain a very rare adverse event linked to Vaxzevria but are well recognized, with ongoing safety monitoring and clinical guidance to manage them effectively. It is important for individuals to be aware of the potential risks and to seek immediate medical attention if any concerning symptoms occur after vaccination.
[1] European Medicines Agency. (2021). Vaxzevria (ChAdOx1 nCoV-19). Retrieved from https://www.ema.europa.eu/en/medicines/human/EPAR/vaxzevria [2] Centers for Disease Control and Prevention. (2021). Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT) and Thrombosis with Thrombocytopenia Syndrome (TTS). Retrieved from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/adverse-events.html [3] World Health Organization. (2021). Adverse events following immunization with COVID-19 vaccines. Retrieved from https://www.who.int/emergencies/diseases/novel-coronavirus-2019/covid-19-vaccines/adverse-events-following-immunization [4] European Medicines Agency. (2021). Safety update for COVID-19 Vaccine AstraZeneca. Retrieved from https://www.ema.europa.eu/en/documents/press-release/safety-update-covid-19-vaccine-astrazeneca_en.pdf
- Despite concerns about rare adverse events such as vaccine-induced immune thrombocytopenia and thrombosis (VITT) or thrombotic thrombocytopenia syndrome (TTS) with the Oxford-AstraZeneca COVID-19 vaccine (Vaxzevria), studies show these incidents are extremely uncommon and most patients who experience them tend to recover.
- The European Medicines Agency (EMA) has added a warning about the potential risk of Guillain-Barré syndrome, a neurological disorder, to Vaxzevria's label, but they cannot yet conclusively determine whether the vaccine directly causes this condition.
- It is important to seek immediate medical attention if one experiences symptoms related to thromboembolic events after receiving the Vaxzevria vaccine, such as shortness of breath, chest pain, leg swelling, abdominal pain, neurological symptoms, and tiny blood spots beneath the skin beyond the vaccine injection site.
