How the Oxford-AstraZeneca vaccine differs from other shots

Latest: Dubai approves Oxford-AstraZeneca vaccine to fight Covid-19

The Oxford-AstraZeneca coronavirus vaccine will be distributed in the UK beginning early January.

The country’s medicines regulator is set to give the green light this week, reports say.

It comes after several other coronavirus vaccines gained approval in various parts of the world, among them shots from Pfizer-BioNTech, Moderna and Sinopharm. In the UAE, the Pfizer-BioNTech and Sinopharm vaccines are already being used.

Here, we look at the Oxford-AstraZeneca vaccine, how it differs from other vaccines and what could be done to improve it.

How does it work?

The vaccine is given in two doses, 28 days apart.

Researchers extracted genetic instructions for building coronavirus spike proteins – the structures on the outside of the virus that it uses to enter human cells – and inserted them into another virus called an adenovirus. The host adenovirus used in the vaccine is a virus that causes the common cold in chimpanzees.

This adenoviral vector, as it is known once new genetic material is added to an adenovirus, has been altered in the laboratory to ensure it cannot infect people and multiply.

Once it enters human cells, through the vaccine, it causes them to produce harmless coronavirus spike proteins. The body’s immune system reacts against these proteins and that response confers protection against the coronavirus.

Essentially it tricks the body into thinking it has been infected with Covid-19.

Other coronavirus vaccines employ similar technology, including Sputnik V from Moscow’s Gamaleya Institute.

While the Oxford-AstraZeneca vaccine involves two doses, based on the same chimpanzee adenovirus, Sputnik V uses two genetically engineered human adenoviruses, each given separately.

Why use adenoviruses?

Adenoviruses are seen as good vectors because they are stable. Once injected into people, they are unlikely to undergo genetic changes.

Chimpanzee adenoviruses are particularly good because humans will not have previously been infected by them. This reduces the risk of something known as adenoviral vector immunity: individuals infected with a particular adenovirus in the past may have developed immunity to the vector itself.

In such cases, when the vaccine is injected, the immune system jumps into action against the adenovirus and it cannot produce the proteins it has been genetically engineered to create. If these proteins are not synthesised, a person’s immune system will not react against them to give immunity to whichever disease the vaccine is supposed to prevent.

So the person has immunity to the vaccine vector but not to the disease.

As well as being used in vaccines, adenoviruses are also useful vectors for gene therapy, in which therapeutic genes are delivered into the cells of people with genetic defects.

Who is behind the vaccine and how have they tested it?

A team of University of Oxford scientists completed their design for the vaccine after Chinese researchers released details of the coronavirus genetic material online early this year.

The university teamed up with British-Swedish pharmaceutical giant AstraZeneca to develop and distribute the vaccine.

Much of the funding came from the British government, which bought up 100m doses in advance.

Clinical trials involving more than 24,000 people took place in Brazil, South Africa and the UK and manufacturing is taking place in more than 10 countries to ensure, as the university put it in November, “equitable global distribution”.

How effective is this 'winning formula'?

In late-stage clinical trials, the vaccine was, overall, 70.4 per cent effective at preventing people falling ill with Covid-19. This figure averages results from two dosing regimens.

With two standard doses, effectiveness was 62.1 per cent. When people were given half a dose, and then a full dose, efficacy was 90 per cent.

In comments to British media published on Sunday, AstraZeneca’s chief executive, Pascal Soriot, said a “winning formula” had been worked out that would achieve results “up there with everybody else" – a possible reference to other vaccines that are as much as 95 per cent effective.

Mr Soriot also indicated the vaccine was completely effective at preventing severe cases of Covid-19.

Scientists not connected with the vaccine programme have suggested that an initial half-dose results in better protection because it reduces adenoviral vector immunity.

What benefits does the vaccine offer?

The vaccine is relatively cheap, costing about £3 (Dh14.7) per dose. Coronavirus vaccines based on messenger RNA, a type of genetic material, such as the Pfizer-BioNTech and Moderna vaccines, are several times more expensive. Another benefit is that it can be stored in a refrigerator and does not require extreme cold temperatures.

“It’s so much easier to store and distribute. Anything you can store at zero and a few degrees above is much easier,” said David Taylor, professor emeritus of pharmaceutical and public health policy at University College London.

Read More

All you need to know about Russia's Covid-19 vaccine Sputnik V

What is the Sinopharm vaccine and how does it compare to global alternatives?

How the Pfizer-BioNTech Covid-19 vaccine works

In addition, the Oxford-AstraZeneca vaccine is thought to produce fewer allergic reactions than some coronavirus vaccines.

How could it be improved?

Aside from Mr Soriot’s comments that AstraZeneca had found an optimum regimen for the vaccine, this month it was announced that scientists were looking at combining it with Russia’s Sputnik V vaccine to increase efficacy.

The idea is that a person could be given one dose of the Oxford-AstraZeneca vaccine and another dose of one of Sputnik V’s two genetically engineered human adenoviruses.

The Russian Direct Investment Fund, which is behind Sputnik V, said trials would begin by the end of the year.

Using the two vaccines may be better than two doses of the same vaccine because it reduces adenoviral vector immunity.