How does the Oxford Covid-19 vaccine work?

Human trials of the coronavirus vaccine candidate being developed at the University of Oxford suggest it is safe and induces an immune response to Covid-19.

Early results indicate the jab could provide double protection – generating an immune response which stimulates the body to produce both an antibody and T-cell response.

But what does the vaccine do, how does it work, and what happens next?

– What is the vaccine? 

The vaccine – called ChAdOx1 nCoV-19 – uses a weakened version of a common cold virus (adenovirus) which causes infections in chimpanzees.

It has been genetically changed so it is impossible for it to grow in humans.

It is hoped the vaccine will make the body recognise and develop an immune response to the spike protein – recognisable in images of the virus – that will help stop Covid-19 from entering human cells and therefore prevent infection.

– What do the preliminary results suggest?

The results of the clinical trials, published in The Lancet on Monday, indicate that the vaccine candidate has triggered two responses in the immune system.

The first is that it stimulates the immune system to produce antibodies – proteins produced by the blood in response to antigens which are harmful substances that come from outside the body, such as from viruses or bacteria – and that it also causes the body to produce T-cells.

If the non-specific immune cells which respond to any invader instantly cannot tackle it, the T-cells come into play.

These cells attack the virus directly.

With questions remaining about the duration of the antibody response to Covid-19, research suggests T-cells have a more important role in offering protection against the disease.

It is not yet known whether the Oxford vaccine candidate provides long-term immunity.

Coronavirus – Fri Apr 17, 2020
Doses of the Oxford Covid-19 vaccine (Sean Elias/University of Oxford)

– Does this mean people can start getting vaccinated against the Covid-19?

No.

Based on their results, researchers say further clinical studies should be done with this vaccine.

The current results focus on the immune response measured in the laboratory, and further testing is needed to confirm whether the vaccine effectively protects against infection.

– How are the trials progressing?

More than 4,000 participants are already enrolled in the UK, with enrolment of a further 10,000 people planned as researchers test the ChAdOx1 nCoV-19 vaccine.

Trials are also taking place in South Africa and Brazil and it is hoped an effective vaccine could be ready later this year.

This trial aims to assess how well people across a broad range of ages could be protected from Covid-19.

HEALTH Coronavirus
(PA Graphics)

– Do enough people in the UK have Covid-19 in order for trials to show efficacy?

Professor Sarah Gilbert, who is leading the Oxford research, has said low transmission rates in the UK mean there is “little chance” of trials in the country proving the effectiveness of a coronavirus vaccine.

A sufficient number of volunteers have to be exposed to the virus to see whether a vaccine protects them or not.

However, if their chances of being in contact with an infected person are low, it will take a long time to demonstrate the efficacy of a vaccine candidate.

– What can be done to combat this?

Researchers have started trialling the vaccine in countries where there is a higher infection rate.

But some are calling for challenge trials, which involve deliberately exposing people to the virus after giving them the vaccine.

A number of prominent scientists, including Nobel laureates, are calling for volunteers to be exposed to coronavirus after receiving a vaccine to see if it offers protection.

They have signed an open letter to the head of the US National Institutes of Health (NIH), saying these challenge trials could accelerate vaccine development.

The signatories, who include Adrian Hill, director of the Jenner Institute at Oxford where the vaccine was developed, are calling on the NIH, its allies, international funders, and world bodies like the World Health Organisation, to undertake immediate preparations for human challenge trials.

– If a successful vaccine is developed, can it be manufactured to scale?

Production of the vaccine has already been scaled up ahead of the trial to prepare as early as possible for potential future deployment.

The Government has signed deals for 90 million doses of promising Covid-19 vaccines, with more in the pipeline.

The latest deal is for vaccines being developed by an alliance between the pharmaceutical giants BioNtech and Pfizer as well as the firm Valneva.

This is in addition to 100 million doses of a vaccine being developed by Oxford University with AstraZeneca.

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