"Booster" vaccinations will begin later this year to fight mutations of the Covid-19 virus, Health Secretary Matt Hancock has confirmed.
It means some people who have already received two vaccinations will be offered a further jab, to ensure they remain protected as the virus changes.
Mr Hancock said the UK was on course to offer a vaccine to every adult by the end of the July - and more than 10 million people have already had their second dose.
The booster shots will be designed to fight mutant strains of Covid, which may be resistant to existing vaccines.
And speaking in the House of Commons, Mr Hancock highlighted concern about Covid variations by announcing India will be placed on the Government's "red list" for travellers.
It means anyone who is not a UK or Irish resident, or a British citizen, will be barred from entering the UK if they’ve been in India in the previous 10 days.
The rules will come into force at 4am on Friday.
Mr Hancock said: "India is a country I know well and love. Between our two countries we have ties of friendship and family. I understand the impact of this decision but I hope the House will concur that we must act."
He said the UK has detected 103 cases of an Indian variant of coronavirus, but the vast majority of cases links to international travel and were picked up by testing at the border.
It means people caught the virus overseas, and the Indian strain does not appear to be spreading in the UK.
Mr Hancock said the samples have been analysed to see if the new variant has any “concerning characteristics” such as greater transmissibility or resistance to treatments and vaccines.
He added: “After studying the data, and on a precautionary basis, we’ve made the difficult but vital decision to add India to the red list.”
However, 557 cases of the South African variant have also been discovered in the UK, mostly in London.
He told MPs: “We’ve already procured enough vaccine doses to begin the booster shots later this year.
"We will be working with our current vaccine suppliers and new suppliers, like the CureVac partnership, to work out which vaccines will be effective as a booster shot and to design new vaccines specifically targeted at the variants of concern – like the variant first found in South Africa."
Mr Hancock also defended the Government's decision to hold a consultation in to whether to make it compulsory for care home staff to be vaccinated.
He said: “The vaccination rate amongst care home staff is currently below 80% in over half of all local authority areas.
“Many care homes have called for vaccinations to be required for those who work in these settings.
"We have therefore launched a consultation into to whether we should require care home providers that care for older adults to deploy only workers who’ve received their Covid 19 vaccination unless they have a medical exemption.”