Covid: What is the Oxford-AstraZeneca vaccine?

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A single shot of the Oxford-AstraZeneca vaccine is highly protective, reducing the chance of someone getting ill and needing hospital treatment by more than 80%.

The findings, from Public Health England are based on people aged over 80 who were some of the first to be immunised in the UK's vaccine rollout.

Scientists say the results are "very strong", and apply to the Pfizer-BioNTech vaccine too.

How does the Oxford vaccine work?

It is made from a weakened version of a common cold virus (known as an adenovirus) from chimpanzees. It has been modified to look more like coronavirus - although it can't cause illness.

Once injected, it teaches the body's immune system how to fight the real virus, should it need to.

• What you need to know about vaccine safety
• How do the Covid vaccines compare?
• When will you be eligible for the vaccine?

Unlike Pfizer's jab - which has to be kept at an extremely cold temperature (-70C) - the Oxford vaccine can be stored in a normal fridge. This makes it much easier to distribute.

Why are some other countries limiting their use of this vaccine?

Some European countries initially offered the vaccine only to 18-64 year-olds because they said there was limited data on how well it protects the over-65s.

Both Germany and France have now reversed this stance, and both now recommend the vaccine for over-65s.

The European Medicines Agency approved the vaccine in January for use in all age groups, including older adults.

AstraZeneca says its trial data suggests it works among over 65s. Earlier studies show older people, as well as younger people, appear to have an equally strong immune response to the vaccine.

Is the Oxford vaccine as good as the Pfizer?

Large trials showed the Pfizer vaccine was 95% effective, while the figure for the Oxford one was 62%.

But directly comparing results is difficult because there are differences in the way the trials were carried out.

And it's important to remember that even the lower 62% figure is a better result than the best flu jab, which is about 50% effective.

No-one who received the Oxford vaccine was hospitalised or became seriously ill due to Covid.

A recent study found a single dose of the Oxford vaccine offered 76% protection for three months, and this went up to 82% after the second dose.

How long do vaccines protect against Covid?

It is not yet known how long protection lasts with any of the coronavirus vaccines.

A study found that unvaccinated people who have had Covid, develop protection for at least six months. Vaccines are likely to provide stronger protection than this.

It may be that people need annual vaccinations, as happens with the flu jab.

Which vaccine will I get?

You will not be given a choice about which vaccine you get.

In the UK, recommendations on which groups get the vaccine are made by the Joint Committee on Vaccination and Immunology.

Does the vaccine protect against new variants?

Experts are studying all of the current coronavirus vaccines to check how well they work against new, mutated variants of the virus that are emerging.

Government's deputy chief medical officer, Jonathan Van Tam, says there is "plenty of evidence" the vaccines appear to be effective against the Kent variant that is dominant in the UK.

There is less evidence about protection for other ones, such as the Brazil and the South Africa variants.

A study based on about 2,000 people with the vaccine, suggests the Oxford-AstraZeneca vaccine offers limited protection against mild and moderate disease caused by the South Africa variant.

South Africa has paused roll-out while it investigates further.

There is no evidence to suggest it would not be effective at preventing more severe cases that need hospital treatment.

In the UK, more than a hundred cases of the South Africa variant have been identified and measures are being introduced to try to limit its spread.

Six cases of the Brazil variant have also been found. One of the six people affected has not yet been identified, but the search has narrowed from the whole country down to 379 households in the south-east of England.

• South Africa variant: What is the risk?
• How worrying is the Brazil variant?

UK scientists are working on new versions of the vaccine, to keep up with a virus that will inevitably keep mutating.

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