A single dose of vaccine gives “majorly enhanced” protection against coronavirus variants in people who have previously been infected with Covid-19, a study has found.

Scientists discovered that, in those who have not previously been infected and have only received one dose of the vaccine, their immune response to variants of concern may be insufficient.

In a new paper published by Imperial College London, researchers looked at immune responses in healthcare workers at Barts and Royal Free hospitals in London following their first dose of the Pfizer/BioNTech vaccine.

They found that people who had previously contracted Covid-19 and had mild or asymptomatic symptoms had “significantly enhanced” protection against the Kent and South Africa variants after the first dose of the vaccine.

Researchers believe it is possible that the findings will apply to other variants in circulation, such as those first identified in Brazil and India.

Speaking at a webinar on Friday, hosted by the Science Media Centre, Rosemary Boyton, professor of immunology and respiratory medicine at Imperial College London, said: “What we found was that you had really, really majorly enhanced responses if you’d had a history of (Covid-19) infection.”

She said they were “in a different league” in terms of immune response, adding: “Prior infection rescues your response against variants.

“You’re much more likely to be protected against the Wuhan strain but also against the variants.”

Prof Boyton, who led the research, said those who have not previously had Covid-19 “made less potent immune responses, that may leave them vulnerable to infection”, adding that this highlighted the importance of a second vaccine dose.

She said of the 731 healthcare workers studied, around 20% had previously contracted Covid-19, the majority of which were infected during the first UK lockdown.

She described natural immunity as “long-lived and sustained”.

Danny Altmann, professor of immunology at Imperial College London, described the immune response of one vaccine dose for those who have not been previously infected as “feeble”, but added that it was still enough to have some impact.

“It’s very weak compared to two doses,” he said.

When asked whether the interval period between two doses of vaccine – which is currently 12 weeks in the UK – should be shortened, Prof Altmann said the research did not have policy implications and “if it ain’t broke, don’t fix it”.

He said: “We’ve got an awful lot of people that are either on zero or one vaccine dose.

“We’ve got a window of vulnerability to be aware of at a time where there are lots of variants of concern around the world.”

Researchers said it remains unclear how much protection is offered by T cells – which recognise and destroy cells infected with coronavirus – but found mutations in the Kent and South Africa variants resulted in T cell immunity which could be “reduced, enhanced or unchanged” compared to the original strain.

It comes as Public Health England (PHE) said on Thursday it had identified two new variants linked to the Covid-19 variant first found in India.

The two variants are designated as “variants under investigation” rather than “variants of concern”.

Earlier this week, the Government announced that an extra 60 million doses of the Pfizer/BioNTech vaccine have been secured for a booster vaccination programme in the autumn.