The Prime Minister said the Covid-19 jab was safe and stressed that the UK’s Medicines and Healthcare products Regulatory Agency (MHRA) was one of the “toughest and most experienced” in the world.
It comes as Germany became the latest country to suspend use of the AstraZeneca vaccine following reports of blood clots in those who have had the shot.
Professor Andrew Pollard, head of the Oxford University vaccine group, said while it was right that regulators investigated reports of such side effects, data from millions of people was “very reassuring” that there was no link.
While on a visit to Coventry on Monday, Mr Johnson was asked for his views on the news that Ireland and the Netherlands had paused the rollout of the jab.
Asked directly if he could tell the public that the AstraZeneca vaccine was safe, he said: “Yes, I can. In the MHRA we have one of the toughest and most experienced regulators in the world.
“They see no reason at all to discontinue the vaccination programme… for either of the vaccines that we’re currently using.
“They believe that they are highly effective in driving down not just hospitalisation but also serious disease and mortality.
“We continue to be very confident about the programme and it’s great to see it being rolled out at such speed across the UK.”
The German government said it was suspending its use of the Oxford/AstraZeneca vaccine as a “precaution” and on the advice of its national vaccine regulator.
According to the European Centre for Disease Prevention and Control, Germany has received slightly more than three million doses of the AstraZeneca vaccine and only used 1.35 million doses so far.
The Netherlands, the Republic of Ireland, Denmark, Norway, Bulgaria, Iceland and Thailand have all temporarily suspended their use of the jab.
Last week, the World Health Organisation (WHO), the European Medicines Agency (EMA) and the MHRA said there was no evidence of a link between the jab and an increased risk of blood clots.
Professor Sir David Spiegelhalter, a statistician from the University of Cambridge, said the decision to pause the AstraZeneca vaccine rollout in some countries, including Denmark, Norway and Ireland, could be doing “more harm than good”.
He told the World At One: “I’ve looked at the AstraZeneca reports and they’ve said that 17 million jabs across the EU and the UK (had been administered) and they’ve had about 15 cases of deep vein thrombosis and 22 cases of pulmonary embolism reported.
“Doing some sums, deep vein thrombosis happens to one in 1,000 people per year of all ages.
“So, out of those 17 million jabs, we would expect at least 17,000 of those people to get a deep vein thrombosis some time in the year.
“So that means that there will have been – and you can pretty well guarantee it – 350 people who have had an AstraZeneca jab then had a deep vein thrombosis in the week following that.”
Meanwhile, Prof Pollard said “safety is clearly absolutely paramount” but that about 3,000 cases of blood clots occur every month in the UK from other causes.
“So, when you then put a vaccination campaign on top of that, clearly those blood clots still happen and you’ve got to then try and separate out whether, when they occur, they are at all related to the vaccine or not,” he told BBC Radio 4’s Today programme.
Prof Pollard said that more than 11 million doses have now been given in the UK, and the MHRA has said “very clearly that they’re not seeing any increase in the number of cases of blood clots” over what they would see normally.
“I think at this moment we’ve got the most data from the UK, which looks very reassuring, but of course it’s absolutely right that there’s careful monitoring of safety and this gets looked into,” he said.
The professor pointed to the “huge risks” from Covid-19 for those who are unvaccinated, adding that “if we have no vaccination and we come out of lockdown in this country, we will expect tens of thousands of more deaths to occur during this year”.
He continued: “A number of countries around Europe are now seeing an increase in cases again.
“Italy and France and Germany and Poland – all have the start of a new surge in cases.
“It’s absolutely critical that we don’t have a problem of not vaccinating people and have the balance of a huge risk – a known risk of Covid – against what appears so far from the data that we’ve got from the regulators – no signal of a problem.”
Elsewhere, Professor Anthony Harnden, deputy chairman of the Joint Committee on Vaccination and Immunisation (JCVI), also sought to reassure the public and said people should attend their vaccine appointments.
He said that the EMA, the MHRA, the WHO and AstraZeneca have “all said this vaccine is safe”.
He told BBC Breakfast: “The data that we look at on a weekly basis on JCVI and a daily basis at MHRA are reassuring that there is no link, so we are right in this country to press on.
“We will keep monitoring this and if there is any safety signals that we are concerned about, we would let the public know straight away.
“At the moment, the message is absolutely clear – go and get your vaccine when offered.
“I spent all yesterday in our practice vaccinating with the Oxford/AstraZeneca vaccine – I would not be immunising my own patients unless I felt it was safe.”
Prof Harnden said analysis of the 11 million doses of the vaccine given so far in the UK had found “no demonstrable difference between the blood clots in those that have been vaccinated from those in the general population.
“We have to remember that there are 3,000 blood clots a month on average in the general population and because we’re immunising so many people, we are bound to see blood clots at the same time as the vaccination, and that’s not because they are due to the vaccination.
“That’s because they occur naturally in the population.
“One ought to also remember that Covid causes blood clots. So, the risks of not having the Covid vaccination far outweigh the risks from the vaccinations.”
Prof Harnden also told the programme that all over-50s in the UK can expect to be vaccinated in the next few weeks.
“Most people over the age of 50 will be vaccinated really within the next few weeks – so it is tremendously successful,” he said of the vaccination programme.
“Those first nine priority groups included 99% of all hospitalisations and deaths, certainly in wave one of the pandemic, so we’re feeling very optimistic.
“We’re seeing a very sharp reduction in the deaths and hospitalisations throughout the country.”
On the issue of side-effects, Prof Harnden said women were more likely to get them from the Oxford/AstraZeneca jab than were men.
“The Oxford/AstraZeneca vaccine – for the first dose – seems to give quite a lot of minor side effects like: a very sore arm; fever; malaise; headache and sometimes chills which may last for up to 48 hours afterwards,” he said.
“They do seem to be more common in women and in younger women.
“With the Pfizer vaccine, which we are given at the moment, it seems to be the reverse – side-effects are more likely with the second vaccine.
“The message is once you’ve had your first Oxford/AstraZeneca vaccine – if you do get some side-effects which are unpleasant, take some paracetamol.”
He said people should not be deterred from having a second dose.
On Sunday, Dr Phil Bryan, vaccines safety lead at the MHRA, said people “should still go and get their Covid-19 vaccine when asked to do so” despite reports from Norway and Denmark about potential cases of blood clots.
“We are closely reviewing reports but given the large number of doses administered, and the frequency at which blood clots can occur naturally, the evidence available does not suggest the vaccine is the cause,” he said.
AstraZeneca also said its own review had found no evidence of an increased risk of pulmonary embolism, deep vein thrombosis (DVT) or thrombocytopenia, in any defined age group, gender, batch or in any particular country.
In clinical trials for the jab, the number of clotting incidents was small and “lower in the vaccinated group” than in those who were unvaccinated, it added.
“To overcome the pandemic, it is important that people get vaccinated when invited to do so,” the firm said in a statement.