A "one shot" vaccine by Johnson & Johnson is expected to get approval soon – and could be used for "hard to reach" groups.
Regulators are expected to authorise the jab shortly, with 30 million ordered for the UK.
Health officials said the one-dose vaccine could be crucial in improving uptake among those who have been reluctant to be vaccinated or proved difficult to get hold of.
Two thirds of adults in the UK have now had their first jab and almost one third have had both, the latest figures show.
The first Johnson & Johnson doses are expected to arrive in July at the earliest, with officials saying they are unlikely to be used in the main rollout of the programme as it moves through younger age groups.
Medical regulators said that so far data suggested the Johnson & Johnson jabs may have a similar safety profile to the AstraZeneca vaccine, which is now largely being restricted to those over the age of 40.
Officials said the Johnson & Johnson jabs could be targeted at those who did not take up original offers for vaccines, including groups such as those who were homeless.
Prof Jonathan Van-Tam, the deputy chief medical officer, said the Johnson & Johnson vaccine, also known as the Janssen vaccine, could help boost uptake.
He added: "It will be authorised as a single dose schedule and that could potentially make it very important, rather than no vaccine, in populations that are hard to reach; basically where you have one chance of vaccinating them and little chance of calling them back for a second vaccine."
Health services have now administered a total of 51.8 million vaccines, including 35 million people with their first dose and 16.7 million with their second.
Matt Hancock, the Health Secretary, said: "This has been a truly national effort, with NHS and care staff and volunteers coming together across the UK to deliver the vaccine at an incredible pace, saving thousands of lives.
"One jab at a time, the approved vaccines are helping to send this virus into retreat, with coronavirus cases and deaths now at their lowest levels since the start of the pandemic. I strongly encourage everyone to take up the offer when it comes so we can put this pandemic behind us."