Covid-19 patients maintain a form of immunity against the coronavirus for at least six months after infection, a new study shows.
The findings may mean people who have already had the virus are less likely to get reinfected if they come into contact with the virus again.
A group of more than 2,000 people working for Public Health England volunteered to take part in the study and donate blood every month, with the first people recruited in early March, before lockdown was announced.
A total of 100 people tested positive for SARS-CoV-2, the virus which causes Covid-19, but none were hospitalised. More than half (56 per cent) had symptoms.
The study focused on a specific type of immune response, called T cells, which are created by the body following infection. They are different to antibodies but are just as pivotal in fighting disease.
The scientists behind the research call their findings encouraging and are ‘cautiously optimistic’ there is long-lasting and robust immunity following coronavirus infection.
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This graph shows the cellular immune response in 100 infected people after six months, The blue bars are level of T cells targeting the viral spike. Blue and purple show other proteins which induce animmune response
A T cell response was detected in all patients, with people who expressed symptoms creating around 50 per cent more T cells than in asymptomatic patients. Pictured, a graph showing the heightened immune response in symptomatic patinets
The UK Coronavirus Immunology Consortium (UK-CIC) worked with PHE on the study and asked colleagues to be tested for the virus and take part in the study.
It has not yet been peer-reviewed and is due to be published to the server bioRxiv soon.
Of the 100 people who tested positive for the virus, 77 were women and the average age was 41. None of the infected participants were older than 65.
The blood samples were taken directly to a lab where they underwent a range of tests to determine the level of immune cells to various proteins found on the virus.
This included cells which target the viral spike on SARS-CoV-2 which allows the coronavirus to infect human cells as well as other proteins found in and on the virus.
All 100 people in the study had detectable T cells after six months. However, the level of antibodies in some participants had dropped below detectable levels.
Speaking today at a press briefing, Professor Paul Moss, study author from the UK CIC and Dr Shamez Ladhani, study author and a consultant epidemiologist at Public Health England, say this does not necessarily mean antibodies have vanished.
Instead, it is more likely the antibody levels have simply dropped below what the current assays can detect.
The researchers add that the level of antibodies needed to fight off a repeat infection remains a mystery.
Antibody concentration below the detection sensitivity of the current tests may well be sufficient, they say.
A study from PHE found T cells – a type of white blood cell in the immune system – are produced by everyone infected with the coronavirus (stock)
Study finds a quarter of patients have LOST antibodies and 4% of England has them
A study published last week found far fewer Britons have coronavirus antibodies now than at the peak of the first wave.
The REACT-2 project — which sends out tens of thousands of DIY blood tests to work out how much of the population has been infected — found 4.4 per cent of people in England in September had Covid-19 antibodies, proteins in the blood trained to fight off the disease.
By comparison, the first round of the study in June found 6 per cent tested positive for antibodies, marking a fall of 26 per cent in three months.
Worryingly, the biggest drop was spotted in the over-65s, who are most vulnerable to falling ill or dying from the disease.
Imperial College London scientists, who led the research, said they suspect natural protection against Covid-19 lasts between six to 12 months. They believe that most people will be vulnerable to reinfection after that time.
Until it is know what specific level of antibodies is needed to fight off infection, it will be impossible to say if this decline and gradual plateau of antibody levels is a cause for concern or not.
‘Early results show that T-cell responses may outlast the initial antibody response, which could have a significant impact on COVID vaccine development and immunity research,’ says Dr Ladhani.
However, a T cell response was detected in all patients, with people who expressed symptoms creating around 50 per cent more T cells than in asymptomatic patients.
The reason for this is unclear. One explanation could be that people who had symptoms created a greater immune response and therefore may be less likely to get infected again.
However, another plausible reason is that asymptomatic individuals are inherently better at fighting off the virus and are therefore less likely to get reinfected.
‘To our knowledge, our study is the first in the world to show robust cellular immunity remains at six months after infection in individuals who experienced either mild/moderate or asymptomatic COVID-19,’ Professor Moss says.
‘Interestingly, we found that cellular immunity is stronger at this time point in those people who had symptomatic infection compared with asymptomatic cases.
‘We now need more research to find out if symptomatic individuals are better protected against reinfection in the future.’
The findings have implications for public health protocols but also for vaccine development.
Of the T cells the study looked for, those which target the viral spike were very common. This spike is the crux of most vaccines in development.
However, the research also revealed other proteins which are abundantly targeted by the T cells, indicating vaccines that target other aspects of the virus could be effective.
Although the impetus is on the viral spike for many vaccines, there are some potential vaccines looking at other aspects of the virus.
‘I want to emphasise that vaccination trials are studying cellular immuinity and data so far shows that this is acheived with the current regimes that are in use,’ Professor Moss syas.
‘It is not the case thst this is neglected by vaccine triallists,’ Professor Moss says.
The researchers say that while this study is encouraging and implies people have come cellular immunity to the virus, it does not mean people can not contract Covid-19 twice.
‘It does not mean you can not get re-infected…’ Professor Moss says.
‘This can not be taken as confirmation of an immunity passport. Absolutely can not do that.’
SARS PATIENTS HAVE T CELLS 17 YEARS LATER
Scientists have found SARS patients still have crucial disease-fighting cells 17 years after infection.
SARS — another type of coronavirus very similar to the one that causes Covid-19 —was behind an epidemic that predominantly struck Asia in 2003. No cases have been identified for 15 years.
But some infected during the outbreak still have key white T cells, suggesting they would be protected from ever getting re-infected.
The study led by Duke-NUS Medical School, in Singapore, published in the scientific journal Nature this week, involved 23 SARS patients.
They collected blood samples and tested whether they still harboured any immune cells that were effective against SARS.
Investigations showed all patients ‘still possess long-lasting memory T cells’ reactive to the virus.
The findings ‘support the notion that Covid-19 patients will develop long-term T cell immunity,’ the researchers wrote.
This could be significant for vaccine research because it helps scientists understand how long a vaccine would protect a person before before another booster shot is needed.
In further experiments, the scientists mixed blood samples with fragments of SARS-CoV-2 to see what happened.
The cells showed ‘robust’ reactivity against SARS-2 in all patients by latching on to them.
To explore the subject of immunity further, 37 volunteers who had never been infected with either SARS-1 or SARS-2 were recruited.
They wanted to see if infection with other human coronaviruses that have been around for centuries offered some kind of protection against Covid-19.
The researchers found ‘remarkable’ levels of T cells able to latch on to the Covid-19 virus in 50 per cent (19) of the participants.
‘Surprisingly, we also frequently detected SARS-CoV-2 specific T cells in individuals with no history of SARS, Covid-19 or contact with SARS/Covid-19 patients,’ the authors wrote.
They believe these T cells may exist due to previous infection with another coronavirus — of which there are seven that can infect humans.