Covid: How does the Oxford vaccine work and how does it compare to Pfizer and Moderna?

The Oxford vaccine is the latest to show promise. Credit: PA

The Oxford University Covid-19 vaccine, which can be up to 90% effective, has been approved by regulators - but how does it compare to others?

The Pfizer version was the first to be cleared - and Moderna's has been given the green light in the US but is still under review here - but the accessibility and easy of use could make Oxford's the most practical.

There are cost and storage burdens related to the first two vaccines, whereas the AstraZeneca/Oxford one is cheaper and is stable at fridge temperature, whereas the others require freezers.

The good news builds on phase two trial data released earlier in the month suggests the jab produces a strong immune response in older adults.

Sarah Gilbert, professor of vaccinology at the University of Oxford explains how the dosages work

It's the latest in positive developments as vaccine progress worldwide continues at an unprecedented pace.

So how does Oxford's iteration of a potential vaccine work and how does it differ to what else is out there?

How does the AstraZeneca/Oxford vaccine work?

The vaccine – called ChAdOx1 nCoV-19 – uses a harmless, weakened version of a common virus which causes a cold in chimpanzees.

Researchers have already used this technology to produce vaccines against a number of pathogens including flu, Zika and Middle East respiratory syndrome (Mers).

The virus is genetically modified so it is impossible for it to grow in humans.

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

When the vaccine enters cells inside the body, it uses this genetic code to produce the surface spike protein of the coronavirus.

This induces an immune response, priming the immune system to attack coronavirus if it infects the body.

Does it differ to Pfizer and Moderna’s vaccines?

Yes. The jabs from Pfizer and Moderna are messenger RNA (mRNA) vaccines.

Conventional vaccines are produced using weakened forms of the virus, but mRNAs use only the virus’s genetic code.

(PA Graphics) Credit: PA Graphics

An mRNA vaccine is injected into the body where it enters cells and tells them to create antigens.

These antigens are recognised by the immune system and prepare it to fight coronavirus.

No virus is needed to create an mRNA vaccine. This means the rate at which the vaccine can be produced is accelerated.

Is it as effective as the others?

The results show that overall the Oxford vaccine is 70% effective.

"The full-dose regimen gave 62% effective but, counterintuitively, those that received the half dose/full-dose regimen had about 90% protection," ITV News Science Editor Tom Clarke says.

US-manufactured Moderna vaccine may prevent 94.5% of people contracting coronavirus, while the Pfizer vaccine stats show it can protect 90% of the popular.

Will it be easy to store?

The Pfizer and Moderna require being kept at frightfully cold temperatures, making them trickier to transport.

Pfizer needs to be stored at -70C, while the Moderna iteration requires to be kept at -4C but maintains stability in a fridge for short periods.

The Oxford vaccine, however, can be stored in a standard refrigerator, making it more practical.

Prof. Gilbert explains why we should not make comparisons between the vaccines

What will it cost?

Unlike the Pfizer and Moderna vaccines, the Oxford AstraZeneca jab is being sold at cost price at around $4 and $5 (£3/£4) a dose; in contrast Moderna said it will be charging $32 to $37 (£24/£28) a dose putting mass vaccination programmes out of financially reach for lower-income nations.

What about antibodies and T-cells?

The Pfizer, AstraZeneca and Moderna vaccines have been shown to provoke both an antibody and T-cell response.

Antibodies are proteins that bind to the body’s foreign invaders and tell the immune system it needs to take action.

A team of experts at the University of Oxford working to develop a vaccine that could prevent people from getting Covid-19 Credit: Sean Elias/PA

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

Nearly all effective vaccines induce both responses.

The Oxford vaccine induces robust antibody and T-cell responses across people of all ages, the data indicates.

Can the Oxford vaccine be manufactured to scale?

Yes. The UK Government has secured 100 million doses as part of its contract, enough for most of the population.

(PA Graphics) Credit: PA Graphics

The head of the UK Vaccine Taskforce, Kate Bingham, has said she is confident it can be produced at scale.

Experts hope the jab could be ready to go and rolled out shortly.

Can this vaccine help the elderly?

There have been concerns that a Covid-19 vaccine will not work as well on elderly people, much like the annual flu jab.

However, data from the Oxford-AstraZeneca trial suggests there have been “similar” immune responses among younger and older adults.

The results show that the vaccine is better tolerated in older people compared with younger adults, and produces a similar immune response in old and young adults.