The study has raised questions over the effectiveness of test to find out who has had Covid-19
According to a recent study not all patients that have been infected with the coronavirus test positive for antibodies.
The study led by researchers at St George's, University of London and St George's University Hospitals NHS Foundation Trust found, has raised questions over the effectiveness of test to find out who has had Covid-19, reported the Independent.
Even though most of the people who have had tested positive for Covid-19 have antibodies in their blood for up to two months, for 177 patients in the study between 2 and 8.5 percent the result for antibodies did not turn positive.
In March, Boris Johnson hailed antibody testing as a "game changer", and several of the tests have been approved for use in the UK. Some also hope that those who have already been ill with Covid-19 may be immune to further infection.
Professor Sanjeev Krishna, one of the lead investigators on the study, said: "A certain number may not actually show they've had an infection. You have to adjust or allow for that in any interpretation of large scale data."
Antibodies are produced by the body immune's system to fight coronavirus and continue to be made after recovery. Tests can therefore show whether someone has had Covid-19. They are separate to a viral test, which shows whether someone currently has the infection.
While a programme of antibody testing was introduced for NHS and care staff late last month, the Department of Health and Social Care made clear the value of such tests was currently limited to "providing data and a greater understanding on the spread of the virus".
The St George's study – which was conducted in association with the Liverpool School of Tropical Medicine, Mologic Ltd and Institut Pasteur de Dakar, Senegal – found that those at higher risk of severe disease were more likely to have an antibody response. That included ethnic minorities, older patients, those who were overweight, and those who had underlying conditions.
Professor Krishna said there was a need for more research to determine whether or not people who do have antibodies are protected from further infection.
"The best way to establish that would be take people who do have detectable antibodies and then see, when they are exposed to infection, just what their chances are of getting another infection. That sort of process would take time and may also take a higher risk of infection than – thank goodness – we have right now."
And he said that while the study offered reassurance in showing that most people who have had the infection continue to make antibodies for at least two months, there were as yet no definitive answers on immunity.
"I'd love to be able to state things with that great certainty that everyone wants to hear," said Professor Krishna.
"The problem is that we've got to be cautious. We're going to have to wait for work where people who have the antibodies are definitely shown to not get an infection again with this virus."