ZimFact is publishing a series of fact guides on Covid-19 vaccines as a contribution to the provision of factual information around a pandemic surrounded by so much misinformation.
The AstraZeneca-Oxford COVID-19 vaccine
The vaccine, officially known broadly as AZD122 and Covishield in India, received the World Health Organisation’s emergency use authorisation on February 15, 2021.
Here is a factsheet on the COVID-19 vaccine commonly known as the AstraZeneca vaccine:
Who developed it?
The vaccine was developed by British-Swedish biopharmaceutical company AstraZeneca, the United Kingdom’s University of Oxford and its spin-off company, Vaccitech.
AstraZeneca has also licenced the Serum Institute of India to produce a version of the vaccine, which is known as Covishield.
AstraZeneca also has an agreement with South Korea’s SK Bioscience to manufacture the vaccine.
What is its actual name?
Now known simply as AZD122, the vaccine was previously known as ChAdOx1 n CoV-2. The former name was derived from the fact that the vaccine is a chimpanzee (Ch) adenovirus-vectored vaccine (Ad), whose development was led by the University of Oxford (Ox) which has been shown to stimulate an immune response to nCoV-19, the novel coronavirus that was first identified in 2019.
How was it developed?
SARS-CoV-2, the virus which causes COVID-19, has spikes on its surface which it uses to enter human cells. It is these protein spikes that most vaccines and treatments target.
The AstraZeneca vaccine is based on the SARS-CoV-2 virus’ genetic instructions for building the spike protein.
However, unlike the Pfizer vaccine, which stores the instructions in single-stranded RNA, the AstraZeneca vaccine uses double-stranded DNA.
The developers added the gene for the coronavirus spike protein to another virus, called an adenovirus, a common cold virus that causes infections in chimpanzees and contains the same genetic material found in the SARS-CoV-2 virus spike protein.
The AstraZeneca-Oxford researchers used a modified version of a chimpanzee adenovirus, which can enter cells, but can’t replicate inside them.
How does it fight SARS-CoV-2, the virus which causes COVID-19?
The AstraZeneca vaccine is a vector virus vaccine. This means it contains a modified version of a different virus than the one that causes COVID-19. Inside the shell of the modified virus, there is material from the virus that causes COVID-19. Once the viral vector is inside the human cells, the genetic material gives the cells instructions to make a protein that is unique to the virus that causes COVID-19. Using these instructions, the cells make copies of the protein. This prompts our bodies to build immunity against the virus, in the event of infection.
Specifically, when the AstraZeneca vaccine is injected into a person’s arm, the adenoviruses are engulfed by human cells. Once inside the cell, the adenovirus travels to the nucleus, where the cell’s DNA is stored.
The adenovirus pushes its DNA into the cell’s nucleus.
While the adenovirus is engineered so it cannot replicate itself inside the cell, the gene for the coronavirus spike protein (inside the adenovirus) can be read by the cell and copied into a molecule called messenger ribonucleic acid, or mRNA.
The mRNA leaves the nucleus, and the cell’s molecules read its sequence and begin assembling spike proteins.
Some of the spike proteins produced by the cell form spikes that migrate to its surface and stick out their tips. These protruding spikes can then be recognized by the immune system, which gets primed to attack the SARS-CoV-2 virus if it later infects the body.
Storage
The AstraZeneca vaccine does not have to be frozen in storage, unlike the Pfizer vaccine. This is because DNA, which forms the basis of the AstraZeneca vaccine is more robust than mRNA used in the development of vaccines such as Pfizer’s. Also, the adenovirus that acts as the vector in the AstraZeneca vaccine has a tough protein coat which protects the genetic material inside. As a result, the AstraZeneca can last for at least six months when refrigerated at temperatures between 2-8 degrees celsius, like most other common vaccines.
Efficacy and effectiveness
Vaccine efficacy and effectiveness are often confused and used interchangeably.
Efficacy measures the performance of a vaccine measured during a clinical trial, while effectiveness refers to how well the vaccine does in the real world.
In November 2020, AstraZeneca announced that the vaccine showed 62% efficacy when given as two full doses at least one month apart.
However, a study by scientists at the South African Medical Research Council Vaccines and Infectious Diseases Analytics Research Unit, published in the New England Journal of Medicine on March 16, 2021, found that the AstraZeneca vaccine was ineffective against a variant of the novel coronavirus first identified in South Africa towards the end of 2020.
“A two-dose regimen of the ChAdOx1 nCoV-19 vaccine did not show protection against mild-to-moderate Covid-19 due to the B.1.351 variant,” the study concluded.
South Africa abandoned plans to roll out AstraZeneca COVID-19 vaccinations in February 2021, after a small study showed the vaccine’s limited efficacy against the virus strain predominant in that country.
Sources: AstraZeneca, Vaccitech, US Centres for Disease Control, WHO, New York Times.
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