People who have previously had coronavirus and have antibodies are unlikely to be re-infected within six months, an NHS study shows.
Research from Oxford University Hospitals examined 12,180 healthcare workers at Oxford hospitals from April to November.
Antibody testing revealed that 1,246 workers had already contracted the virus when the study started, but none had symptoms. Only three (0.24 percent) of these people later tested positive, and none of them developed symptoms.
Researchers say the study indicates ‘previous SARS-CoV-2 infection offers protection against short-term reinfection’.
Antibody testing revealed that 1,246 workers had already contracted the virus when the study started, but none had symptoms. Only three of these people later tested positive and none had symptoms
Regular testing also revealed 89 of the 11,052 people who had not been infected before later developed an infection and symptoms.
An additional 76 employees who had not previously been infected then tested positive but were asymptomatic.
In total, 168 (1.49 percent) of those without prior infection either continued to test positive for the disease or exhibit symptoms.
The study, published online today as a pre-trial, shows that people who have already been infected are highly unlikely to catch the virus again.
One of the authors of the paper, Professor David Eyre of the University of Oxford’s Nuffield Department of Population Health, said: ‘This ongoing study involving a large group of healthcare professionals has shown that infection with COVID-19 provides protection against re-infection for most for at least six months.
A study had previously found that antibody levels drop rapidly after infection and reach half of their original number after only 85 days (pictured). However, the latest study encourages that the base level of the antibody is sufficient to prevent reinfection
RESPECT: THE TRUTH OF COVID IMMUNITY, ANTIBODIES AND T-CELLS
Antibodies are substances produced by the immune system that store memories of how to fight a particular virus.
They come in various forms and can attack viruses and destroy themselves or can force the body to produce other forms of immune cells and white blood cells to perform the dirty work for them.
They can only be created if the body is exposed to the virus by being properly infected, or through a vaccine or other form of specialist immunotherapy.
Once antibodies are created – the body essentially shapes them around a virus when it encounters one in the blood – the body usually retains a memory of how to make them and which ones go with which virus.
In general, antibodies produce immunity to a virus because they are relocated if it enters the body a second time and defeats the bay faster than it can take hold and cause a disease.
Researchers are still unsure of the truth about immunity because Covid-19 has only been around since January – meaning its long-term effects are still unclear.
So far, cases of people being infected more than once have not been numerous or convincing.
With some diseases like chickenpox, the body can remember exactly how to destroy it and be able to ward it off before the symptoms start if it gets back in the body. However, so far it is unclear how long Covid-19 patients have been protected.
Evidence is beginning to suggest that antibodies disappear as little as eight weeks after infection with coronavirus, scientifically called SARS-Cov-2.
However, antibodies are only one type of substance that can produce immunity. The immune system is a large tissue of proteins that have various functions to protect the body from infection.
T cells – which cannot be detected by the ‘have you had it’ antibody test – made in response to the infection, can offer a form of immunity that lasts several times longer.
T cells are a type of white blood cell that is a key component of the immune system and helps fight disease.
Other scientific studies have shown that people who have had a cold in the last two years have T cells that show ‘cross-reactive protection’ against Covid-19.
‘We found no new symptomatic infections in any of the participants who had tested positive for antibodies, while 89 of those who had tested negative got the virus.
‘This is really good news because we can be sure that at least in the short term, most people who get COVID-19 will not get it again.’
A study had previously found that antibody levels drop rapidly after infection and reach half of their original number after only 85 days.
The decline continues and the amount of antibodies drops below detectable levels in most people 137 days after their maximum reading.
But Professor Eyre says the latest finding shows that there is some immunity in those who have been infected.
Following the previous study, concerns were raised that antibody levels might fall too low and recovered Covid-19 patients would be vulnerable to reinfection.
However, it is possible that the reduction in antibody levels does not mean that they disappear, just that they fall below the detectable level.
Also, if the concentration of antibodies is extremely low, the immune system has a memory function called B cells, which remembers how to make the antibodies and churn them quickly if it recognizes the virus again.
Oxford clinicians say it is too early to say whether there is long-term protection beyond six months, but call the results ‘encouraging and exciting’.
Dr Katie Jeffery, Director of Infection Prevention and Control at Oxford University Hospitals, said: ‘This is an exciting finding that indicates that infection with the virus provides at least short-term protection against reinfection – this news comes in the same month as other encouraging news about COVID -vaccines.
‘I would like to thank all our staff who have shown great commitment to participating in our clinics for repeated cotton swab and antibody testing to keep our patients and each other safe.’
A separate study published earlier this month looked at the complete cellular response in Covid-19 patients after infection.
A group of more than 2,000 people working for Public Health England volunteered to take part in the survey and donate blood each month, with the first people recruited in early March before the shutdown was announced.
A total of 100 people tested positive for SARS-CoV-2, the virus that causes Covid-19, but none were hospitalized. More than half (56 percent) had symptoms.
All 100 humans had high Covid-specific T cells six months later, reflecting the results of the most recent antibody study, but the number of antibodies in this cohort had dropped to below detectable levels.
Dr Shamez Ladhani, co-author of this paper, said at the time: ‘Early results show that T cell responses can survive the initial antibody response, which can have a significant impact on COVID vaccine development and immunoassays.’