Asked how the MHRA regulatory body has been so quick to approve the vaccine, Dr June Raine stresses its standards are equivalent to all international standards.

"The public can be absolutely confident the standards we have worked to are the equivalent of those around the world," she says.

How long is the lag before the vaccine becomes effective?

Prof Sir Munir Pirmohamed says people will be immune seven days after the second dose.

There will be partial immunity after the first dose, he says, explaining they have seen some protection occurring after day 12 of the first dose.

Prof Wei Shen Lim, chair of the Joint Committee on Vaccination and Immunisation, is asked how prioritisation of the vaccine was decided.

He says prioritisation was based on the risk of dying from Covid-19 and "in order to protect the most vulnerable we have prioritised the most vulnerable individuals first".

He says the other element was protecting the NHS and the health and social care system “because by protecting the NHS we also protect lives”.

Dr June Raine is asked by the BBC's Fergus Walsh whether she can reassure the public they can have "absolute confidence" in the vaccine given how quickly it has been approved.

She says the way of working in a rolling review ensures teams of clinicians and scientists are working in parallel to complete all the work according to strict guidelines on safety, effectiveness and quality.

"This vaccine has only been approved because those strict tests have been done and complied with and everyone can be absolutely confident that no corners whatsoever have been cut," she says.

She adds that the MHRA started preparing for the process in June and so was "ready for that last sprint".

Robert Cuffe
BBC head of statistics

Life is about balancing risks – the small chances that something bad might happen if you cross the road or don’t wear a face covering or get a new vaccine.

So what can we say about the risks that we’re balancing here?

So far this year, just over one in 1,000 people in the UK have died with coronavirus involved.

That’s an average. Your risk drops if you’re young, healthy, white or a woman.

But the vaccine will likely be given first to people for whom the risk is much higher.

If a serious vaccine side effect happened to 1 in 1,000 people who took it, it would very likely have shown up in the 40,000 volunteers who took part in the studies.

And the scientists charged with monitoring the study haven’t reported any serious safety concerns.

Of course, when a vaccine is first approved, we can’t rule out very rare problems.

But the MHRA approved the vaccine because the benefits outweigh the risks.

Prof Wei Shen Lim says in phase one of the programme, the JCVI hope that 90-99% who are at risk of dying from Covid-19 will be covered.

The JCVI recognises that there may be “operational reasons” why the prioritisation of the vaccine might need to be more flexible, he adds.

He finishes by saying: “Overall we have good news today, we have a vaccine that is acceptably safe and effective. Good vaccine uptake will save lives.”

Professor Sir Munir Pirmohamed goes on to say the safety of the vaccine is similar to other vaccines.

Most of the side effects are very mild and last only a day or so, he adds.

He says his group were visited by NHS colleagues who spokes about deployment strategies and his group were able to advise them.

He said it would be important to undertake surveillance as people are vaccinated, which will include monitoring them.

He added that no testing is required before receiving the vaccine.

Prof Wei Shen Lim has been setting out the order of which groups will be prioritised for the first rollout of the vaccine, which is illustrated in the slide below:

It is now the turn of Prof Wei Shen Lim, who is chairman of the Joint Committee on Vaccination and Immunisation, which decides the order in which people will get the jab.

He says the UK is fortunate in that it has “one of the best immunisation programmes in the world” and he says that expertise has informed the committee.

The JCVI has recommended that for the first phase of the vaccination programme to protect people “who are most at risk of dying from Covid-19”, as well as to protect health and social care services.

Now, Professor Sir Munir Pirmohamed, the chair of the Commission on Human Medicine Expert Working Group, is speaking at the Downing Street briefing.

He starts by thanking the members of his group, including a variety of experts, who worked tirelessly to analyse all the data available on the vaccine.

He says they looked at raw data which allowed them to look at the risk/benefit analysis of the vaccine. They also looked at laboratory data, manufacturing process data, as well as clinical data, and found there was an "overwhelming benefit" for this vaccine, and therefore recommended its use.

Dr June Raine, chief executive of British regulator the MHRA, says a rolling review has been used to complete the assessment of the vaccine because "time is of the essence".

But she stresses "that doesn't mean that any corners have been cut".

"The safety of the public will always come first," Dr June Raine says, and she emphasises the recommendation has only been given following the "most rigorous scientific assessment of every piece of data".

Dr June Raine, chief executive of the MHRA, has been explaining the different stages for the Covid vaccine, set out in the slide below:

Dr June Raine, chief executive of British regulator the MHRA, says the regulator's recommendation to approve the Pfizer/BioNTech vaccine for use has been reached following "an extremely thorough and scientifically rigorous review of all the evidence of safety, of effectiveness and of quality".

The Downing Street technical briefing on the Pfizer/BioTech vaccine is just starting.

This is the first and most important question scientists ask when they start designing and testing a new vaccine or treatment.

Safety trials begin in the lab, with tests and research on cells and animals, before moving on to human studies.

The principle is to start small and only ever move on to the next stage of testing if there are no outstanding safety concerns.

As long as the safety data from the labs is good, scientists can check that the vaccine or treatment is effective too. That involves tests on large numbers of volunteers.

All of the work and findings are checked and verified independently.

The Covid vaccine trials have happened at breakneck speed, but they haven't skipped any of these steps.

Approval will only be given for a vaccine if the government regulator (the Medicines & Healthcare products Regulatory Agency or MHRA) is happy that it's both safe and effective.

Read more.

We're expecting a Downing Street technical briefing on the Pfizer/BioNTech vaccine announcement at around 10:00 GMT.

We'll be hearing from Dr June Raine, chief executive of British regulator the MHRA, Prof Sir Munir Pirmohamed, chair of the Commission on Human Medicine Expert Working Group and Prof Wei Shen Lim, chair of the Joint Committee on Vaccination and Immunisation, which advises UK health departments.

Image source, Getty Images

In case you're just joining us, here are some of the biggest stories from around the world:

• The United Nations has voted unanimously for a resolution calling on all countries to designate seafarers as key workers. Due to travel restrictions, hundreds of thousands of maritime workers have been left stranded aboard ships worldwide, unable to return home
• France has said it will carry out random checks at borders to help curb infections. It comes amid tensions with Spain and Switzerland, where ski slopes are expected to remain open during the winter
• Poland has become the 13th country in the world to surpass one million confirmed cases of coronavirus, according to a tally by Johns Hopkins University
• The US Centers for Disease Control and Prevention has said it will shorten the recommended length of quarantine after exposure to someone who is positive with coronavirus. The Anerican public health body said it will soon issue guidelines which reduce the number of days from 14 to between 7 and 10.

Image source, Science Photo Library

When you can get a vaccine will mainly depend on your age - with people in care homes and the over-80s at the front of the queue, potentially being vaccinated this month.

The Joint Committee on Vaccination and Immunisation (JCVI) has decided that care home workers and health and social care staff are also a priority, because they could transmit the virus to vulnerable patients.

After these groups, the plan is to offer the vaccine to everyone else based on their age - from the oldest to the youngest by next spring.

You'll be invited to get a vaccine as soon as it's your turn, probably by letter or text.

This could be through your GP surgery, a hospital or care home if you work there, or through vaccination hubs which are being set up around the country.

You can read more more about how the vaccine will be rolled out here.

Away from vaccine developments, the other main story in England today is the end of the national lockdown and the return to a tiered system of restrictions.

The new system, which is tougher than the one in place before the lockdown, came into force today - just hours after being approved by MPs in a Commons vote.

The government said the move would help "safeguard the gains made during the past month", despite 55 Tories voting against the plan.

More than 55 million people are in the strictest two tiers and cannot mix indoors with those in other households.

Non-essential shops and other businesses, including personal care services such as hairdressers and beauty salons, can now reopen for the first time in four weeks.

Pubs and restaurants can also reopen in tier one and two areas, although in tier two alcohol can only be served with a "substantial meal".

Now a vaccine has been approved, attention will turn to getting as many people vaccinated as possible - and a strong public health message will be paramount.

On ITV's Good Morning Britain, presenter Piers Morgan suggested to the health secretary one way to do that would be to get vaccinated live on television.

"Yeah, I'll take it with you, Piers," said Matt Hancock.

The presenter said he would meet Mr Hancock "anytime next week, if we can do this".

"Let's do it together, live on air. It would be powerful, it would send the right message," he added.

Mr Hancock replied: "We'd have to get that approved because, of course, there is a prioritisation according to clinical need and, thankfully, as a healthy, middle-aged man, you're not at the top of the prioritisation."

But, he added, he was "up for doing it" if people thought it was reasonable, and if it helped to persuade others to take the vaccine, "it's worth it".