A fourth coronavirus vaccine has been approved for use in the UK and needs just one dose, rather than two.
The first deliveries are expected to arrive in the country from later this year now the jab has been authorised by the Medicines and Healthcare products Regulatory Agency (MHRA).
The Vaccine Taskforce originally secured 30 million doses, based on the predicted clinical need at the time.
But given the scale and pace of the vaccine rollout in the UK the government has decided to amend its original order and there are now just 20 million on the way.
What kind of vaccine is it?
Developed by Johnson & Johnson's pharmaceutical arm, Janssen, the jab is an adenovirus vaccine.
These are based on weakened versions of adenoviruses, which are a group of viruses that typically infect membranes of the eyes, respiratory tract, urinary tract, intestines and nervous system, and include the common cold.
How does it work?
Like the Oxford/AstraZeneca jab, the J&J vaccine uses viral vector technology where a modified version of a different virus is used to deliver instructions to the body's cells to trigger the immune system to begin producing antibodies.
Were there not concerns about the vaccine being linked to blood clots?
The European Medicines Agency (EMA) said there is a "possible link" between Johnson & Johnson's Covid-19 vaccine and very rare blood clots.
But it concluded that the overall benefits of the vaccine "outweigh the risks of side effects".
J&J previously confirmed it would delay rollout of its single-dose vaccine across Europe after the US paused its administration to investigate reports of potentially dangerous blood clots.
The Joint Committee on Vaccination and Immunisation will submit updated advice for the Janssen vaccine before doses become available.
What other vaccines does the UK have?
So far the Moderna, Pfizer/BioNTech and Oxford/AstraZeneca vaccines are being administered in the UK.
The approval of the J&J vaccine comes as it is thought that the most vulnerable groups of people, including the elderly, will be offered a booster jab before the winter.
