Covid: What is the Oxford-AstraZeneca vaccine?

Use of the Oxford-AstraZeneca vaccine has been paused in a number of European countries after a small number of blood clots were reported among people who had recently had the jab.

Germany, France, Italy and Spain are among the countries to have suspended its use. The World Health Organization (WHO) is investigating the reports, but says there is no evidence that the clots were linked to the vaccine.

The UK's medical regulator also says the jab is safe to give to people.

There is no evidence that the Oxford-AstraZeneca vaccine is unsafe.

Blood clots can occur naturally and are not uncommon.

About 17 million people in the EU and the UK have received a dose of the vaccine, with fewer than 40 cases of blood clots reported as of last week. This is no more than would be expected in the normal course of events.

The European Medicines Agency (EMA) is expected to issue a decision on the continued use of the vaccine on Thursday.

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.

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.

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.

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.

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 then reversed this stance, and recommended the vaccine for over-65s, before the latest decision to pause its use across all age categories.

The EMA 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.

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.

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.

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, while 10 cases of the Brazil variant have also been found.

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