In previous posts, we have decoded the J&J vaccine as well as the mRNA vaccines (you can find more information here and here). Now, the AstraZeneca Vaxzevria COVID-19 vaccine will be discussed.
The idea behind the vaccine is still very similar – We want to train our immune system to recognize the spike protein so that, when it comes across the real COVID-19 virus, our immune system can recognize and fight it. In this case, the AstraZeneca vaccine used a non-replicating chimp adenovirus as a vector [1,2]. The adenovirus family typically causes colds but, in this case, they used a weakened virus that is unable to replicate. This virus is the transport system to deliver the “information” or “cargo”.
What “cargo” does it deliver? The “cargo” includes the gene for the coronavirus spike protein. Overall, these would be the main steps of the process [3]:
After the vaccine shot, the vector goes inside our body, carrying the “cargo”.
Then, the genetic information of the spike is given to the cell nucleus, where it is transcribed into mRNA. More information about this process here.
Afterwards, the spike protein is produced in the cytoplasm and temporarily expressed in the cell surface, so that our immune system learns to recognize and respond to it.
The DNA fragment, the vector, and the mRNA are quickly broken down and cleared by our bodies [3].
It should be noted that, since the vector mainly contains the spike protein sequence (not the rest of the coronavirus genome), it cannot cause COVID-19 [1]. Moreover, considering that the adenovirus is non-replicating, it is quickly cleared by our system.
The AstraZeneca COVID-19 vaccine showed strong antibody and cellular responses. In some studies, the vaccine efficacy was detected to be around 70% [4]. The European Medicines Agency also included a list of common side effects, such as: headache; muscle pain; fever; and others [5]. In some cases, the vaccine can be related to decreased levels of blood platelets (thrombocytopenia) and, rarely, with thrombosis (blood clots) [5]. Even though the blood clots are uncommon, some countries or institutions preferred to suspend the vaccine (you can find more information here, based on the data of April, 2021) [6]. Other institutions may prefer to compare the pros and cons of the vaccine (the risk of side effects versus the benefit of being protected against COVID-19), considering each person’s medical history and their physician’s advice.
It is important to note that, depending on your medical history, it might be beneficial to take a different type of COVID-19 vaccine. For example, according to EMA, people with capillary leak syndrome or history of post-vaccine thrombosis with thrombocytopenia should not get the Vaxzevria [5]. Therefore, you can discuss your medical history with your doctors, so they recommend the best vaccine for you.
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Written by: Nicole
Edited by: María and Natasha
BioDecoded is a volunteer group committed to sharing accurate scientific information. 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. 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:
Covid: How does the Oxford-AstraZeneca vaccine work? BBC (2022). Available at: https://www.bbc.com/news/health-55302595 (Accessed: 21 April 2022).
Astrazeneca COVID-19 Vaccine. CDC (2021). Available at: https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-2021-01/02-COVID-Villafana.pdf (Accessed: 21 April 2022).
COVID-19 Vaccines: Viral Vector-based Vaccines. Public Health Ontario (2022). Available at:https://www.publichealthontario.ca/-/media/documents/ncov/vaccines/2021/03/covid-19-focus-on-viral-vector-based-vaccines.pdf?la=en (Accessed: 21 April 2022).
Voysey, M. et al. (2021) “Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomized controlled trials in Brazil, South Africa, and the UK”, The Lancet, 397(10269), pp. 99-111. Available at: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)32661-1/fulltext
Vaxzevria (previously COVID-19 Vaccine AstraZeneca) – European Medicines Agency (2021). Available at: https://www.ema.europa.eu/en/medicines/human/EPAR/vaxzevria-previously-covid-19-vaccine-astrazeneca(Accessed: 21 April 2022).
Why Canada is suspending use of AstraZeneca vaccine in people under 55 | CBC News (2022). Available at: https://www.cbc.ca/news/health/canada-suspends-astrazeneca-vaccine-covid-19-1.5968657 (Accessed: 21 April 2022).
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