A Harvard study has also showed that people who have had a combination of vaccines and natural infection have "substantially higher antibody responses" than people who have only been vaccinated.
"They have very good levels of protection," Dr Ali adds.
"Because each time you are exposed to the vaccine or the virus, you develop an immune response."
'It's not a hard shield'
Although most people develop some level of immunity from getting the virus naturally, it is not guaranteed, Dr Deepti Gurdasani warns.
"Neither natural infection nor vaccination should be seen as a hard shield," the clinical epidemiologist at Queen Mary University tells Sky News.
"You get more varying levels of immune response from natural infection than you do from vaccination.
"Not everyone who gets infected naturally seroconverts [produces an immune response]."
She also says lower immune responses are more common in people who get no or mild symptoms, as well as children and young people.
"Some don't produce immune responses at all," she adds.
"If you have had two doses and a natural infection - you have got some boosted immunity, but the protection you get from both is just a layer - it's not absolute."
Boosters, tests and hand washing important for Christmas
As Christmas approaches, with more socialising and case rates still considerably high, experts have warned the UK is facing a tough winter - and the NHS being overwhelmed.
And with immunity waning a few months after getting a second vaccine, both scientists are urging people to get booster jabs if they are eligible.
"There is more and more evidence that this [coronavirus] is a three-dose vaccine," Dr Gurdasani says.
"Lots of people are at the stage now where they're three or four-months post-vaccination and are getting breakthrough infections.
"It highlights the importance of boosters and of seeing each thing you do, whether that be a test, wearing a mask or recovering from infection, as a layer of protection - not absolute protection."
Dr Ali adds: "The most important thing is still to have the vaccine, but it's also true that the vaccine isn't 100% effective.
"So if you're mixing with vulnerable or elderly relatives over Christmas, basic interventions like taking a lateral flow test and washing your hands regularly are still important".