Covid survivors who get reinfected have lower viral loads and are less likely to suffer symptoms, official data suggested today.
Scientists claim the figures — taken from an analysis of almost 20,000 Britons — are proof the disease is becoming milder.
Studies show infected people who have lower viral loads are less likely to become ill and spread the virus.
Last April, the Office for National Statistics (ONS) began examining people who had been struck down with Covid to determine the risk of them catching it again.
Of the 19,470 people they studied between April 2020 and July 2021, 195 went on to catch Covid for a second time.
This equated to just one per cent of people being reinfected.
The Office for National Statistics studied 195 Brits and found their average Ct value when they caught Covid for the first time was 24.9. The Ct value shows how much of the virus was present in the nose or throat sample, with a lower number equating to a higher amount of the virus. When participants caught Covid again, they had an average Ct value of 32.4, meaning there was less virus present in their sample
Indian variant is 46% more likely to cause reinfection than Kent strain, PHE warns – but only 1.2% of the 80,000 cases studied were caused by reinfection
People who have previously beaten Covid are now more likely to be reinfected because of the Indian variant, an official report has found.
Public Health England said the risk was 46 per cent higher with the Delta variant compared to the previously dominant Kent ‘Alpha’ variant.
The finding was based on real-world analysis of the third wave in England and looked at about 80,000 Delta cases.
But even with the increased risk posed by the mutant strain, the numbers of Britons getting reinfected still remains low.
Of the Delta cases PHE analysed over the past three months, just 1.2 per cent were identified as possible reinfections.
The results follow a lab study earlier this month which found the variant was able to dodge antibodies from previous infection better than earlier strains.
PHE said the reinfection risk was incredibly low in people who had recovered from Covid in the past six months.
The agency looked at the PCR test results for a group of people, both vaccinated and unvaccinated, who had a positive Covid test at least 90 days earlier.
There were 83,197 people who tested positive in the 11-week period of the analysis, of whom 980 were possible reinfections.
Comparing the results to the second wave, it said the risk of being reinfected with Delta was 46 per cent higher than Alpha. The analysis adjusted for different variables including age and vaccination.
Experts aren’t sure how long immunity from previous infection from Covid lasts because the virus is so new.
It is believed that for the vast majority of people, immunity lasts for at least six months.
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Today’s report only looked at people who tested positive at least 90 days after their first positive swab and had negative tests between the first and second infection.
Government statisticians looked at cycle threshold (Ct) values of volunteers, and compared the average scores between the first and second infection.
Ct values show the amount of SARS-CoV-2 virus presented in a swab sample taken, with a lower value equating to a higher viral load.
Only a quarter of those participants who were reinfected had a high viral load — considered to be a score below 30.
For comparison, two-thirds had a high viral load from their first test.
Overall, the volunteers’ average Ct value at their first positive test was 24.9, while it was 32.4 for their reinfection.
Among the group, 93 of them had symptoms the first time they were infected, while just 38 had symptoms the second time they caught the virus.
Scientists say the findings are proof that immunity — from both jabs and natural infections — is kicking in.
Nearly 37.5million adults have had both doses of jabs made by either Pfizer or AstraZeneca.
No vaccine is perfect and many people who are fully-inoculated are still at risk of getting infected.
But the current crop of jabs being used in Britain have drastically slashed the risk of infected people becoming ill.
Meanwhile, the spread of the virus through the population has allowed natural immunity to build up over time, too.
Nearly 6million people have tested positive for the virus over the course of Britain’s three waves — but millions more will have been infected.
Professor Jonathan Ball, a virologist at the University of Nottingham, told MailOnline we ‘shouldn’t be too surprised’ by the ONS findings.
He said: ‘These findings show past infection results in immunity that provides good, but not absolute, protection from reinfection, at least over a relatively short time period.
‘Even in those people who were reinfected, the levels of virus in their nose and throat were lower compared to viral loads seen during a first infection.
‘This suggests that their pre-existing immunity, whilst not preventing infection, does effectively dampen down virus replication second-time around.
‘This is important because it means people reinfected are less likely to suffer serious disease, and also the chances of them passing on the virus to others is reduced.’
He added: ‘We think vaccines will produce even higher levels of protection, even in those previously infected, so I would still urge everyone invited to get both doses of vaccine.
‘I don’t think this is because the virus has become less virulent, it’s more to do with host immunity generated following infection.’
While high Ct values represent a low viral load, scores can vary over the course of infection and a single figure may not provide the most accurate picture.
And not every score can be compared accurately because different labs might not use the same test.
It comes after a separate report last week claimed people who have beaten Covid are now more likely to be reinfected because of the Indian variant.
Public Health England said the risk of reinfection was 46 per cent higher with Delta compared to the previously dominant Kent ‘Alpha’ variant.
The finding was based on real-world analysis of the third wave in England and looked at about 80,000 Delta cases.
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