People who have both had Covid-19 and been vaccinated against it are seven-times more immune than those just to receive the jab, new research suggests.
But the government-funded PITCH study also concluded 99 per cent of patients were well protected after a single dose of the Pfizer-BioNTech vaccine regardless of previous infection, reports the Mirror Online.
A second dose boosted immunity levels and is thought to produce longer-lasting protection, it added.
The findings appear to support the UK strategy of delaying the second dose.
Pfizer had warned a delay of more than two weeks had not been tested in its clinical trials.
Despite this, UK regulators concluded that – based in part on how other vaccines react – a single dose should provide sufficient initial protection.
Today’s data seems to confirm that.
Many other countries have focused on giving both doses within two weeks, meaning half as many people could be vaccinated in the first months of the vaccination rollout.
Researchers at the universities of Oxford, Birmingham, Sheffield, Liverpool and Newcastle found robust T-cell and antibody responses in 237 healthcare workers on average four weeks after the first dose.
Analysis indicated levels of protection offered by a single dose of the Pfizer vaccine were equivalent to a natural coronavirus infection – with immune responses being 6.8 times stronger in those who had previously tested positive for the virus.
Scientists believe these people are better protected against dangerous new variants.
The study also showed a previous infection followed by a single dose left people three times more protected than someone who has not had Covid-19 but had received both doses.
It demonstrates levels of protection are likely to be much higher in those who have had the virus.
The findings suggest that, after vaccination, this group is less likely to suffer any symptoms or pass on the virus – although this was not measured in the study.
Secretary of State for Health and Social Care Matt Hancock said: “The PITCH study presents further proof that vaccines provide excellent protection against the virus.
“Thanks to the incredible efforts of our vaccination programme, over half of all adults in the UK have had the jab, and we remain on track to offer all adults a vaccine by the end of July.
“The vaccine has already saved thousands of lives in the UK.
“A second vaccine jab is crucial for longer-term protection, regardless of whether you have previously had Covid-19 or not.
“I urge everyone to make sure they attend their second appointment to keep themselves and those around them safe.”
Dr Thushan de Silva, study author from Sheffield University, said: “Our study is one of the largest and most comprehensive accounts of the immune response to one dose of Pfizer-BioNTech vaccine comparing previously infected and infection-naive individuals.
“Our results demonstrate that T cell and antibody responses induced by natural infection are boosted significantly by a single dose of vaccine.
“There are some individuals who have a good T cell response and some individuals who have a good antibody response.
“This emphasises the point that it is very important to look at both these arms of immunity when we think about vaccines.”
Co-author Prof Miles Carroll, of Oxford University, said: “What you find is that even if they’ve been previously infected and had one dose, some people may have a really good response.
“Some people may have a mediocre immune response. So having that second dose even if you weren’t previously infected is essential to ensure that you’ve got good solid immunity.
“It is likely that a second dose will increase the longevity of response even if you’ve got prior infection. So the advice would always be to have that second dose.”
Almost 30 million UK adults have now been inoculated and most over-80s who received a Covid jab early on had the Pfizer vaccine.