- Florencia Adeline Adiwinata
The AstraZeneca COVID-19 Vaccine Explained
Updated: Sep 4, 2021
After being halted for two weeks from its first arrival in Indonesia, the AstraZeneca COVID-19 Vaccine has finally been distributed on Monday, March 22, 2021. However, its presence still leaves some minds wondering: what is it made from? Is it safe to use? If you too have similar questions, then it is your lucky day: this article sums up the information known to this day regarding the newest currently-in-use vaccine.
The AstraZeneca COVID-19 Vaccines (source: https://www.bbc.com/news/)
AstraZeneca COVID-19 vaccine is developed by the Oxford University and a Sweden pharmaceutical company AstraZeneca. The vaccine, also known as AZD1222, is a nucleic acid vaccine that contains a snippet of the SARS-CoV-2 gene inside a modified chimpanzee adenovirus. This differentiates it from the first-wave vaccine, Sinovac of China, which uses the whole weakened virus as its content. The AstraZeneca vaccine comes in two doses, given within a span of 4-12 weeks between doses. This vaccine is still undergoing clinical trials in several countries such as the United Kingdom, Brazil, and South Africa. The latest report from the World Health Organization (WHO) states that the AstraZeneca vaccine has overall efficacy of 63.1%.
Some vaccines, such as the Pfizer-BioNTech and Moderna vaccines, use RNA as its nucleic acid component, but the AstraZeneca vaccine contains DNA, which is more structurally-stable than RNA. Therefore, the AstraZeneca vaccine is easier to store: it does not have to stay frozen and can be stored in standard refrigerators for six months. Such characteristics also make it convenient for a wide range of distribution.
Every infecting agent has a feature that indicates its foreignness, known as the antigen. Injecting antigens to your body will trigger the immune system into making antibodies to fight them. In nucleic acid vaccines, antigens are carried within vaccine-delivery media called vectors. Vectors are usually other viruses that have been altered and cleared from their harmful traits.
In SARS-CoV-2, the antigen is its spike glycoprotein. It covers the virus’s membrane and acts as the binding agent to human cells, particularly to the ACE2 receptor. The AstraZeneca vaccines contain a strand of the DNA that corresponds to the formation of this spike. When injected, this DNA will affect our healthy cells into producing similar proteins, therefore establishing antigens that will be detected by the immune cells. As for the vector, the AstraZeneca vaccine uses adenovirus, a virus that causes mild respiratory illness in human adults. Adenoviral vectors can trigger innate and adaptive immune responses when inserted to human bodies. They are also relatively easy to manipulate and suitable for mass-producing. The adenovirus contained in the AstraZeneca COVID-19 Vaccine was modified so that it cannot replicate inside human bodies. Utilizing viruses to fight viruses might sound unconvincing, but the SARS-CoV-2 DNA strand and its adenoviral vector have been carefully remodeled so that they are noticeable to the immune cells but not strong enough to cause an infection. If only, the usage of this combination provokes more alerting signals and doubles the immune response, which is a favorable result.
The antiviral mechanism of the AstraZeneca COVID-19 Vaccines (source: https://covid19vaccinetrial.co.uk/about)
The Use of Trypsin
Another issue that emerged among Indonesians was the claim of porcine trypsin usage in the AstraZeneca vaccine, which the company has denied. Regardless, it is necessary to understand the role of trypsin in vaccine production. Adenovirus containing the SARS-CoV-2 genetic material is cultivated in the genetically-modified human embryonic kidney (HEK) 293 cells which grow in adherent culture. Adherent cell lines grow on surfaces of the vessels or media used in culturing them; thus, they need to be dissociated to obtain the yield cells. This process is called cell passaging, and it is when trypsin comes to use.
Trypsin is a proteolytic enzyme obtained from the pancreas. There are other options of cell culture passaging enzymes but trypsin is widely chosen for its ability to passage strongly adherent cells. In producing vaccines, it is common to use animal-derived trypsin rather than human trypsin to avoid carryover of contaminants that might trigger unwanted side-effects. If the animal-derived trypsin is somehow contaminated, it has a lower chance of affecting human cells, therefore reducing infection risks. The trypsin enzyme is fully discarded after the passaging is complete, then the recombinant adenoviruses are collected from the cells. Altogether, the enzyme does not affect the virus or the resulting vaccine.
Right now, vaccination is our best shot in combating the COVID-19 pandemic. While some issues are still uncertain, better insights will unfold as clinical trials continue. If you have not got the chance to vaccinate, sticking to the health protocols is the best thing that you can do. This is not a battle we can win individually, so take care of yourself and others around you. Stay safe!
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European Medicines Agency. 2021. COVID-19 Vaccine AstraZeneca: benefits still outweigh the risks despite possible link to rare blood clots with low platelets - European Medicines Agency. [online] Available at: <https://www.ema.europa.eu/en/news/covid-19-vaccine-astrazeneca-benefits-still-outweigh-risks-despite-possible-link-rare-blood-clots> [Accessed 23 March 2021].
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World Health Organization (WHO) (2021) ‘Interim recommendations for use of the AZD1222 ( ChAdOx1-S [ recombinant ]) vaccine against COVID- 19 developed by Oxford University and AstraZeneca’, 1222(February), pp. 1–7.
World Health Organization (WHO). 2021. WHO statement on AstraZeneca COVID-19 vaccine safety signals. [online] Available at: <https://www.who.int/news/item/17-03-2021-who-statement-on-astrazeneca-covid-19-vaccine-safety-signals> [Accessed 23 March 2021].