Here's our health correspondent Catherine Burns.

There's no such thing as a vaccine that is 100% effective for every single person.

Researchers trying to find a vaccine for coronavirus was set a target to make it at least 50% effective.

This Oxford vaccine averages out at about 70% so it's done that and then some.

So how does it stack up against other vaccines?

Well, there's a range flu tends to be about 40 to 60% effective at the other end of the scale, chickenpox is about 98% effective for Children.

The important thing to remember is that this vaccine has been shown to be highly effective.

Some people are asking how concise, I insist, be so confident in a vaccine they've come up with in less than a year.

Ah, lot of it comes down to cash.

There's been a huge global effort with massive amounts of money, but also brainpower.

Thes vaccines that we're seeing now have been through all the usual processes just streamlined.

And remember, this isn't from a standing start.

We're dealing with a Corona virus.

Scientists have been studying them for years and knew what the possible weak spots could be.

More than 10,000 people have had this vaccine.

So far.

None has had any serious issues.

There are the kind of side effects you might expect after a vaccine, a sore arm, maybe a headache, temperature or feeling a bit flu.

We for a few days.

The team behind this point out that normally vaccines that are regulated in Europe might have safety data on 3 to 5000 people, and they have thousands more than that have been following them for months.

So far, we've had a few teams of scientists assessing how effective their vaccines are.

In other words, how good it they as stopping people from getting sick with coronavirus.

What we don't know yet is how long they'll offer that protection for another unknown is how good they'll be at stopping the virus spreading, for example, if someone is infected, doesn't have any symptoms but could still pass it on to other people.

There are some early positive signs on this from the Oxford trial, though.

If you want to pick which vaccine you'll be given, the short answer is no slightly longer.

Answer is that the UK government has ordered 100 million doses of the Oxford vaccine more than any other, so it's most likely you'd get this one.

The next question is when?

Well, first of all, it's got to be approved by the regulator on once that happens, there are about four million doses ready to be shipped out so we could see some of them before Christmas.

Realistically, those first doses are going to go to the most vulnerable, probably people in care homes over 80 and health workers.

After that, it will get rolled out across the rest of the winter and spring on.