Video report by Lise McNally
A world-first study to find out if different types of Covid vaccines can be mixed is underway in Liverpool.
Medics at the city's School of Tropical Medicine will give shots of the Oxford/AstraZeneca and the Pfizer jabs several weeks apart. It is one of several sites across the country carrying out the tests.
The nurses carrying out the vaccinations are part of the schools Well Travelled Clinic - they have swapped their regular work vaccinating people ready for travel abroad, and are now working as part of the wider team's coronavirus research.
More than 800 people have volunteered to take part. The first results from the 13-month-long study are expected by the summer.
One of the leading figures in the trial, Dr Andrea Collins, says it is an "opportunity to see if there is any benefit in using the available vaccines interchangeably."
Even if the research shows promise, medical regulators would still need to approve 'mix and match' vaccinations.
Dr Helen Hill, Co-Prinicpal investigator, said: "We don't know the availability of vaccines at this stage.
"We don't know if there'll be enough of the Pfizer vaccine, or the Oxford vaccine, at any given time, so when we get this data, it will help inform the whole of the roll-out programme, in terms of, which are the best options.
"We've already got some data that shows the oxford vaccine is protective against the most common new strain that's emerged, so we can still learn if any other vaccines are similarly protective, and as new strains start to come into the UK we'll be able to monitor that as well."
One of the people taking part in the trial said: "I read about it online, it's something that is interesting, I'm looking forward to doing the study, and I think it's great, because somewhere along the line we need to get out of this pandemic, and this is the best way out.
"We've had a year of lockdown, and really it's something we all need to do if we can.
"And with it being The School of Tropical Medicine, I told myself - well, its one of the leading researchers, and I look forward to doing it for the next year."
The trial is still looking for volunteers to take part over the next year, find out more here.