The Oxford-AstraZeneca COVID-19 vaccine was created by the University of Oxford and its British-Swedish pharmaceutical company partner, AstraZeneca.
On December 30, the UK became the first country to approve the shot.
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Independent scientists have confirmed that the vaccine is “safe and effective” at preventing symptomatic COVID-19, according to preliminary results from its phase three trials published in The Lancet in early December.
Phase three is a large trial involving thousands of people, to prove the vaccine protects people.
The United Kingdom-made vaccine is significant because it is cheaper than the other two major shots being produced by Pfizer-BioNTech and Moderna.
Unlike its main competitors, it can be stored at a regular fridge temperature.
With the availability of more established Oxford technology, the vaccine is also easier to mass-produce and AstraZeneca has promised not to profit from it during the pandemic.
Pfizer-BioNTech’s product costs around £15 per dose ($20), Moderna’s is about £25 ($33), and the Oxford-AstraZeneca vaccine is available at a much cheaper price of around £3 ($4).
The vaccine can be stored, transported and handled for at least six months at 2-8 degrees Celsius (35-46F).
Pfizer and Moderna have a success rate of around 95 percent.
Interim data suggests the Oxford-AstraZeneca vaccine has an average efficacy of 70.4 percent, a figure which could be as high as 90 percent if the dose is adjusted.
“The results show that the vaccine is effective against COVID-19, with in particular no severe infections and no hospitalisations in the vaccine group,” said AstraZeneca Chief Executive Officer Pascal Soriot.
The efficacy rates vary because the preliminary data examined two different ways to administer the vaccine.
In one group, patients were given a placebo which consisted of a smaller initial dose of the vaccine followed by a larger booster dose one month later. Surprisingly, data analysis found that the vaccine was about 90 percent effective at preventing COVID-19 in this group.
In the second group, patients were given the same dose in both instances, producing a lower efficacy rate of 62.1 percent.
It is yet unclear why a smaller initial dose performs better. But scientists have suggested it could be because a larger initial dose prompts the body to produce antibodies against the vaccine itself.
Another reason could be that a smaller initial dose triggers memory cells, preparing the body to produce antibodies in greater amounts when the second larger dose is administered.
The Pfizer-BioNTech and Moderna vaccines are based on messenger RNA (mRNA) technology.
Oxford-AstraZeneca’s is different – it is an adenovirus-vectored vaccine taken from a common cold that normally infects chimpanzees.
Although it has been genetically modified to avoid infection in people, it carries only a part of the coronavirus called the “spike protein”.
Once the vaccine is injected into human cells, it triggers an immune response against the spike proteins, producing antibodies and memory cells which destroy infected cells.