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Explainer: What we know about the Oxford/AstraZeneca vaccine

Developers have applied to the European regulator for authorisation.

Image: PA

THERE HAS BEEN some positive movement on the Covid-19 vaccine front in recent days with a second vaccine arriving in Ireland and a third applying for EU approval.

The first delivery of the recently-approved Moderna vaccine arrived in Ireland yesterday.

And it was confirmed that Oxford/AstraZeneca vaccine developers have submitted their application for authorisation to the European Medicines Agency (EMA).

Here’s what we know about this particular vaccine so far…

First, a refresher on the Pfizer and Moderna vaccines

Both of these vaccines are what’s known as ‘messenger RNA’ (mRNA) vaccines. Before the Covid-19 pandemic, a mRNA vaccine had never been approved before. 

Many traditional vaccines can involve injecting people with weakened forms of the virus. With mRNA vaccines, only the genetic code of the virus is used.

The vaccine enters cells and tells them to create antigens, which are recognised by the immune system. This trains the immune system to recognise and attack the coronavirus if it ever actually encounters it. 

Source: PA

So how does the Oxford/AstraZeneca one work?

This vaccine is what’s known as a viral vector vaccine.

It uses a harmless, weakened version of a common virus which causes a cold in chimpanzees. The virus has been genetically modified so that it is impossible for it to grow in humans – people who get the vaccine will not become ill with a chimpanzee cold.

Scientists transferred the genetic instructions for the coronavirus’s specific ‘spike protein’ – which it needs to invade the cells – to the vaccine.

Once the vaccine enters cells inside the body, it uses this genetic code to produce the surface spike protein of the coronavirus and this induces an immune response.

The immune system is then primed to attack the coronavirus if it infects the body at some point afterwards.

This technology has already been used to produce vaccines against a number of pathogens such as flu, Zika and Middle East Respiratory Syndrome (Mers).

Unlike the Pfizer and Moderna vaccines, this one does not require those ultra-cold temperatures, which would make delivery and storage of the vaccine easier and would better facilitate a mass roll-out. It is also cheaper to produce. 

How effective is it?

Phase 3 trial data showed the jab was 70.4% effective on average across two different dose regimes. It is possibly up to 90% effective with a combination of a half dose, followed by a second full dose. 

In the UK, the regulator has recommended people should receive two full doses, administered with an interval of between four and 12 weeks. 

The vaccine has been shown to provoke both an antibody and T-cell response. Antibodies tell the immune system to take action when a virus is identified. 

T-cells are a type of white blood cell which hunt down infected cells in the body and destroy them. 

A study of the AstraZeneca vaccine found that levels of T-cells peaked 14 days after vaccination, while antibody levels peaked after 28 days. 

The developers have said the vaccine induces a strong immune response in all adult age groups. 

coronavirus-mon-jan-11-2021 Patients receiving the Oxford/AstraZeneca Covid-19 vaccine at the NHS vaccine centre that has been set up in the grounds of the horse racing course at Epsom in Surrey. Source: PA

What do the studies say about side effects?

The first full peer-reviewed efficacy results for a Covid-19 vaccine were published in The Lancet journal in December and this data related to the Oxford/AstraZeneca vaccine.

Just three out of 23,745 participants over a median of 3.4 months experienced serious adverse events that were possible related to the trial.

Just one of these events was in the Covid-19 vaccine group – participants in the control group were given either meningococcal conjugate vaccine or saline. This one event was a case of transverse myelitis, which is inflammation of a section of the spinal cord. 

The trial was temporarily suspended when this occurred but in September the UK’s Medicines Health Regulatory Authority (MHRA) said it was safe to continue the trial. 

In December developers said all three participants who had experienced serious adverse events possibly linked to the trial had recovered or were recovering. 

The majority of side effects associated with the vaccine are the common side effects seen in any vaccination such as redness or pain at the injection site. The UK has not reported any serious adverse incidents with this vaccine since its roll-out. 

Why is it taking so much longer for us to get it than in the UK?

First, bear in mind the EMA cannot give the green light to a vaccine until the developers submit their application for authorisation – and they did not do this until yesterday.

The UK is no longer tied into the EU regulatory system and its own regulator and government is making arrangements independently. 

The EU has been quick to point out that the UK’s regulator has granted a temporary authorisation of supply of the vaccine in the emergency use setting, which is distinct from a marketing authorisation.

“A conditional marketing authorisation (CMA) follows a controlled and robust framework providing safeguards that emergency use authorisations might not. In reality, an emergency use authorisation is not an authorisation of the vaccine but an authorisation of the temporary use of the unauthorised vaccine,” the Commission explained in an article published in December.

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In order to speed up the regulatory process, the EMA has been conducting rolling reviews of vaccine candidates, analysing the data as it becomes available rather than waiting until an application for authorisation has been submitted. 

On 31 December, the EMA said additional scientific information on issues related to quality, safety and efficacy of the vaccine was deemed necessary to support the rigour required for a conditional marketing authorisation. It said this had been requested from the company. 

The request for more information may be connected to an error during an early phase of the trials. 

Some volunteers initially received a half-dose in error, which Oxford attributed to a change “in the manufacturing process”.

When the mistake was uncovered, the drug maker, in consultation with regulators, decided to administer the accidental procedure – a half-dose followed four weeks later by a full dose – to 3,000 of the subjects as part of the larger Phase 3 trials.

This dosage appeared to result in higher efficacy (around 90%) than the two full dose regime. Almost 9,000 participants were given two full doses, also four weeks apart and efficacy was 62%.

This data, it should be noted, was preliminary. It is likely, considering an application has now been submitted to the EMA, that more complete data on the ongoing trials has also been submitted in relation to dosage and subsequent efficacy.

Are there any more vaccines likely to be approved?

The European Commission also has contracts with Johnson & Johnson, Sanofi-GSK and Curevac. 

The Johnson & Johnson vaccine developers are likely to submit their application to the EMA this month. This is a one-dose vaccine, which could help speed up a mass roll-out. Like the Oxford/AstraZeneca vaccine, it uses the viral vector approach. 

In November Sanofi and GSK announced their vaccine would be delayed until the end of 2021 after interim results showed a low immune response in older adults. 

Curevac began final Phase 3 trials in December, with more than 35,000 volunteers in Europe and Latin America. Although the vaccine uses similar mRNA technology to the Pfizer/BioNTech and Moderna vaccines, developers say it can remain stable for at least three months at normal fridge temperatures. 

The company recently joined forces with pharmaceutical giant Bayer. The firms said this would allow Curevac it to tap into Bayer’s expertise and established infrastructure and facilitate the level of supply required if the vaccine is approved. 

Negotiations are also underway for a contract with Novavax.

- With reporting from PA.

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