The UK has "more than enough" doses of Pfizer and Moderna jabs for under-30s, Health Secretary Matt Hancock has told Sky News.
Yesterday it was announced that Britons aged 18-29 would be given an alternative to the Oxford-AstraZeneca vaccine where possible, due to concerns over a possible link between the jab and rare blood clots.
Mr Hancock has said the government is being "totally transparent" with the public about side effects linked to the vaccine, even if they are "extremely rare".
He added that it was "absolutely right" that the government was upfront about the risks and had made the appropriate changes to the vaccination programme in the UK.
He said the 8.5 million 18-29 year olds who are waiting for their jabs will be able to say if they would prefer to have the Pfizer or Moderna vaccine.
He told Sky News: "There are 10.16 million people aged 18-29 in the UK, 1.6 million of them have already had their first jab.
"Anybody who’s had the jab should continue with the second jab because there’s no evidence of this affect after a second jab and we have more than enough Pfizer and Moderna vaccine to cover all of the remaining 8.5 million people aged between 18-29 if necessary."
However, Mr Hancock insisted the Oxford-AstraZeneca vaccine is safe for all ages.
"What we’ve learned in the last 24 hours is that the rollout of the vaccine is working, we’ve seen that the safety system is working, because the regulators can spot even this extremely rare event – four in a million – and take necessary action to ensure the rollout is as safe as it possible can be," he said.
"And we are seeing that the vaccine is working. It’s breaking the link between cases and deaths."
He added: "The speed of the vaccination programme is not affected by the decisions yesterday. You can see and be reassured by the fact we’re taking an abundance of caution and we’re making sure we’re rolling this out in the safest way possible."
He insisted the UK remained "on track" to hit the target of all adults being offered the jab by the end of July.
According to the Medicines and Healthcare products Regulatory Agency (MHRA), up to 31 March, there have been 79 reports of blood clots accompanied by low blood platelet count in the UK, all in people who had their first dose.
Of these 79, 19 people have died, although it has not been established what the cause was in every case.
The 79 cases occurred in 51 women and 28 men, aged from 18 to 79.
Of the 19 who died, three were under the age of 30, the MHRA said.
The risk works out at one in 250,000, or 0.0004%.
People aged under 30 who have already received the first dose of the Oxford-AstraZeneca are being urged to have the second dose to ensure they are properly protected.