The AstraZeneca vaccine has been temporarily suspended in several countries while institutions analyze the association between the vaccine and blood clots. On April 7th, 2021, the European Medicine Agency (EMA) reported that rare blood clots could be an unusual side effect of the AstraZeneca Vaccine – Vaxrezvia [1]. When blood coagulates to a semi-solid form, it can form a clot and end up blocking a vessel. Although most cases occur in women under 60 years old [1], there is ongoing vigilance to determine specific risk factors. Therefore, do we have to worry about blood clots when getting vaccinated?
Considering the dangers of COVID-19, the benefits of the vaccine outweigh the possibility of negative side effects [1]. Even though the estimates vary by country, the chances of having a blood clot after vaccination are incredibly low [2]: The overall risk has been estimated as 4 in a million. What does this number mean? Imagine flipping a coin and getting heads. It would be weird if you flipped the coin 18 consecutive times and always got heads, right? The chances of getting heads 18 times in a row are roughly 4 in a million. What about daily events? In the United Kingdom [3], 17 deaths per million are the odds of dying on a motorcycle after driving 100 miles (161 km). Then, the chances of dying in a motorcycle accident per 100 miles would be greater than the odds of having a blood clot after the COVID-19 vaccine.
It is also important to remember that other common medications have risks associated with different types of blood clots and they are still taken daily by millions of individuals. For example, some hormonal birth control options can increase the risk of blood clots by three to nine times [4].
We should also put this risk into perspective. If we do not get vaccinated, we will not develop protective responses against the SARS-CoV-2 virus, which puts us and those around us at risk for infection. Although mortality rates vary by age group and medical condition, cases of COVID-19 are associated with a 2% to 3% fatality rate [5]. Furthermore, COVID-19 infection can have several short and long-term effects. Some common symptoms are difficulty breathing; dizziness; fatigue; joint and chest pain; or loss of taste and smell. Other symptoms that are more uncommon include neurological and mood alterations; inflammatory syndrome; increased risk for blood clots; as well as heart, lung, and liver damage [6,7,8]. It is important to note that 1 in 20 hospitalized patients from COVID-19 infection develop blood clots [9]. Thus, getting a severe COVID-19 infection is much more dangerous than the side effects from the vaccine.
Although the chances of developing a blood clot following vaccination are low, it is important to monitor any symptoms to avoid future complications. In the weeks following vaccination, the EMA recommends seeking urgent medical attention if you have any of these symptoms [1]: chest pain, leg swelling, blood spots under the site of injection, persistent belly pain, shortness of breath, or neurological symptoms (blurred vision or headaches).
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Written by: Nicole
Edited by: María and Natasha
BioDecoded is a volunteer group committed to sharing accurate scientific information about vaccines. We cannot offer any specific health advice. If you have any doubts about getting vaccinated due to previous health conditions, please speak with your healthcare professional or family physician. Do not forget to inform your doctor about any medications (including birth control or those bought over the counter) that you are currently taking. Your doctor can revise your medical history and advise you on the best path to follow. If you have any questions about this topic, please comment or send them to our email.
References:
Agency, E. M. AstraZeneca’s COVID-19 vaccine: EMA finds possible link to very rare cases of unusual blood clots with low blood platelets. (2021). Available at: https://www.ema.europa.eu/en/news/astrazenecas-covid-19-vaccine-ema-finds-possible-link-very-rare-cases-unusual-blood-clots-low-blood.
Schnirring, L. Groups find possible link between AstraZeneca COVID vaccine, blood clots | CIDRAP. Available at: https://www.cidrap.umn.edu/news-perspective/2021/04/groups-find-possible-link-between-astrazeneca-covid-vaccine-blood-clots. (Accessed: 26th April 2021)
Spiegelhalter, D. & Pearson, M. Understanding uncertainty: Small but lethal | plus.maths.org. (2010). Available at: https://plus.maths.org/content/os/issue55/features/risk/index. (Accessed: 26th April 2021)
Keenan, L., Kerr, T., Duane, M. & Van Gundy, K. Systematic Review of Hormonal Contraception and Risk of Venous Thrombosis. Linacre Q. 85, 470–477 (2018). Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6322116/
Cao, Y., Hiyoshi, A. & Montgomery, S. COVID-19 case-fatality rate and demographic and socioeconomic influencers: worldwide spatial regression analysis based on country-level data. BMJ Open 10, e043560 (2020). Available at: https://bmjopen.bmj.com/content/10/11/e043560
Pero, A., Ng, S. & Cai, D. COVID-19: A Perspective from Clinical Neurology and Neuroscience. Neurosci. 26, 387–391 (2020). Available at: https://pubmed.ncbi.nlm.nih.gov/32713251/
Salehi, S., Reddy, S. & Gholamrezanezhad, A. Long-term Pulmonary Consequences of Coronavirus Disease 2019 (COVID-19). J. Thorac. Imaging 35, W87–W89 (2020). Available at: https://pubmed.ncbi.nlm.nih.gov/32404798/
Carfì, A., Bernabei, R. & Landi, F. Persistent Symptoms in Patients After Acute COVID-19. JAMA 324, 603 (2020). Available at: https://jamanetwork.com/journals/jama/fullarticle/2768351
Rabson, M. Coronavirus: Doctors say getting COVID-19 poses much bigger risk of blood clots | CTV News. (2021). Available at: https://www.ctvnews.ca/health/coronavirus/doctors-say-getting-covid-19-poses-much-bigger-risk-of-blood-clots-1.5353995. (Accessed: 27th April 2021)
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