ITV News Science Editor Tom Clarke explains the latest on the AstraZeneca vaccine
"What people should do is look at what the MHRA say, our independent regulator - that's why we have them, that's why they are independent," the prime minister said while visiting AstraZeneca's manufacturing plant in Macclesfield.
"Their advice to people is to keep going out there, get your jab, get your second jab."
It follows reports that the UK's medicines regulator is considering changing its advice about giving young people the AstraZeneca vaccines amid concerns about blood clots.
The Medicines and Healthcare products Regulatory Agency (MHRA) is said to be reviewing its guidance for under-30s amid concerns the risk of extremely rare blood clots could be marginally higher among younger people.
Channel 4 News reported two senior sources had revealed the MHRA was being urged to ban the jab, developed with Oxford University, in younger people - with a decision expected as early as this week.The MHRA said last week it had identified 30 cases of rare blood clot events out of 18.1 million doses of the jab administered up to March 24.
But the regulator has said the benefits of the vaccine in preventing coronavirus far outweigh any risks and urged people to continue to get their jab when invited to do so.
World Health Organisation director of regulation and prequalification, Dr Rogerio Pinto de Sa Gaspar, said said there is "no link for the moment" between the Oxford AstraZeneca vaccine and blood clots.
He told a briefing: "The appraisal that we have for the moment, and this is under consideration by the experts, is that the benefit-risk assessment for the vaccine is still largely positive."
He added: "For the time being there is no evidence that the benefit-risk assessment for the vaccine needs to be changed and we know from the data coming from countries like the UK and others that the benefits are really important in terms of reduction of the mortality of populations that are being vaccinated."
He said that by the end of Wednesday or Thursday, he expected "we might have a fresh conclusive assessment from our experts".
A number of countries across Europe moved to pause the rollout of the vaccine following reports of blood clots, but the EU's medicines regulator ruled the jab is safe and several countries chose to resume vaccinations.
The prime minister added that it was “very important to stress that the best thing of all is to vaccinate our population, get everybody out getting the jab, that’s the key thing and that’s what I would advocate, number one”.Mr Johnson also spoke about the idea of Covid certification, which would prove whether someone has been vaccinated, has recently tested negative, or is not able to pass on the virus after recently catching it.
He said the government is looking at "the role of vaccination passports for overseas travel", which was "going to be a fact of life, probably".
On domestic Covid certificates, he said ministers are "going to look at the role of a number of signals that you can give that you are not contagious", such as immunity as a result of having had Covid-19, vaccination status and testing as factors.
Pilots will soon carried out at large-scale events, such as the FA Cup semi-finals, to assess whether they can be useful.
Vaccines minister Nadhim Zahawi said if a review, being carried out by Chancellor of the Duchy of Lancaster Michael Gove, finds they could be useful, then the government will put the idea to a vote in Parliament.
The government is facing the real prospect of a rare defeat in the House of Commons over the issue, with more than 70 MPs ready to oppose the proposals in any vote.
It is thought at least 41 Tories would reject Covid certification, while Labour has not yet decided which way it would vote, with shadow health secretary Jon Ashworth telling ITV News the party needs convincing.
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