Antibodies fall by half in less than 90 days after infection with coronavirus, new research at Oxford University Hospitals (OUH) NHS Foundation Trust suggests.
The ongoing study of OUH staff, published as a preprint and still subject to peer review, also showed that virus antibodies last longer in people who have had symptoms and fade quicker in asymptomatic people.
By measuring antibody responses in the same healthcare workers for up to six months, researchers followed what happens to antibody levels over time and how this varied between different people.
Antibodies are proteins produced by a type of white blood called lymphocytes. Pathogens have proteins on their surface called antigens. When a pathogen infects the body, the lymphocytes recognise these antigens as foreign and attack them by producing antibodies.
They found that in this cohort of healthcare workers, antibody levels rose to a peak at 24 days after the first positive COVID-19 test. They then began to fall.
Those tested had lost their positive antibody result after an average of 137 days, the study suggests.
The researchers also found that increasing age, Asian ethnicity and prior self-reported symptoms were associated with higher maximum antibody levels. By contrast, younger adults’ antibody levels fell faster and peaked lower.
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“These findings could be significant: current studies that are using antibodies to assess how many people have been infected in a population might have missed some who have been infected, especially younger people and those infected early in the pandemic and with mild or asymptomatic infection,” co-author Professor David Eyre, of the University of Oxford’s Nuffield Department of Population Health, said.
“The longer-lived antibodies in older people of working age are intriguing and not completely explained.
“This is still a new disease and we are learning more and more about it all the time. But longitudinal studies like ours are needed to answer some of these important questions about how long and at what level antibodies last, and the extent to which they protect people from reinfection.”
The paper presents six months of data from a longitudinal study measuring the level of pathogens in the blood of 3,217 healthcare workers who have attended more than once for antibody testing.
They were among some 10,000 staff across OUH’s four hospitals who were tested both for COVID-19 and for antibodies to give an accurate picture of who among the OUH workforce had been infected.
When looking at 452 healthcare workers who tested positive, over an average of 121 days, the scientists found the average estimated antibody half-life was between 81 and 90 days.
“Since the outbreak of COVID-19, the trust and the university have pooled their resources to develop highly reliable PCR and antibody testing to support the research and care in the fight against the virus,” OUH chief executive Dr Bruno Holthof said.
“I would again like to thank all the people who work at our hospitals who have taken part in this long-term study, which will continue to reveal valuable information about this virus which we are still learning about.”
The study is a collaboration between OUH and the University of Oxford with support from the NIHR Oxford Biomedical Research Centre.
Researchers say ongoing longitudinal studies are required to track the long-term duration of antibody levels and their association with immunity to SARS-CoV-2 reinfection.
How can I protect myself from the coronavirus when shopping?
You’ll have seen signs in your local supermarket advising you to keep two metres from others while moving around the store. This is key to reducing your chances of catching the virus while shopping.
The coronavirus SARS-CoV-2 is spread through respiratory droplets that leave our mouth and nose when we cough, sneeze, or sometimes even talk. The droplets sprayed out by an infected person will contain the virus, which could then enter your body via your mouth, nose or eyes (this is why you shouldn’t be touching your face).
Respiratory droplets don’t usually travel more than one metre, so by keeping two metres from others, you’ll reduce the likelihood of being in the firing line. To make it easier to keep your distance, try to shop during off-peak hours, choose a store that’s limiting the number of people who can be inside at any one time, and use self-checkout if you can.
Keeping your hands clean is the other main thing you can do. If possible, wipe the trolley or basket handles with a disinfectant wipe when you arrive at the store. When you get home, wash your hands or use hand sanitiser before and after unpacking your bags.
A US study found that the coronavirus can survive for up to 24 hours on cardboard, and up to three days on hard, shiny surfaces such as plastic, so wiping down your purchases with a disinfectant spray or a soapy cloth before you put them away is another good habit to get into.
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