England's deputy chief medical officer Professor Jonathan Van-Tam said there was no evidence of increased risk of blood clots with the AstraZeneca jab, adding that "vaccines don't save lives if they're in fridges".
Professor Van-Tam was joined by Health Secretary Matt Hancock in reassuring the public about concerns to do with the vaccine.
Health Secretary Matt Hancock says data shows that after a single dose of the vaccine protection against getting Covid-19 is about 60%, protection against hospitalisation is about 80% and protection against death is about 85%.
He says the data also shows if you live with someone who has been vaccinated you have a 30% lower risk of catching Covid-19.
Speaking today Professor Van Tam said: "Behind the scenes, there is a lot of work going on to look at whether there is a signal in relation to what we call venous thromboembolic events, clots, VTE for short.
"There's a lot of evidence emerging now that is reassuring, that there is no overall excess signal or increased risk.
"I expect, without prejudice to their absolute findings, those to be the final conclusions of the EMA and the MHRA in due course.
"So, no evidence of increased risk, but as you heard from Professor Ramsay, a lot of evidence that the vaccine is actually saving lives.
"That's the really important thing, that we push on with this, and I think from the enthusiasm of the patients I've vaccinated, I see the enthusiasm of the British people to push on with this.
"Because vaccines don't save lives if they're in fridges. They only save lives if they're in arms, and that's a really important fact."
Mr Hancock also said all those over-50 would be invited to get their first dose of the vaccine from today.
He said there would be a focus on vaccinating the most vulnerable before moving on to the over-40s but warned the UK would do "everything necessary" to ensure supplies continue.
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He told the Downing Street press conference: "We're on track to offer a first dose to everyone in priority groups 1-9 by April 15. While we deliver on that commitment, we also want to ensure that this offer reaches everyone in groups 1-9.
"At the same time as opening up offers of vaccinations to all those who are 50 or above, we are going to do whatever it takes to reach all those in the most vulnerable groups who haven't come forward yet before we move onto the next cohort, which is people in their 40s.
"Before we forge ahead I want us to be confident that we've done everything we can to protect those most in need of protection and we will do all we can and do everything necessary to deliver the supplies that are contractually committed to protecting people in this country."
