Virus infection may not guarantee antibody response

UP TO one in 12 people who has had coronavirus will not develop antibodies but those who do still have them two months later, research suggests.

The health service has begun rolling out antibody tests, which is hoped will show who has previously had the disease, and whether they have become immune to it.

However, scientists are unclear about the degree of protection and how long it lasts, meaning that, so far, it is not been possible to develop “immunity certificates”, which show who is protected against the virus.

The new study shows that Covid-19 antibodies remain stable in the blood of the majority of infected people almost two months after diagnosis, and possibly longer.

But the research found that antibodies were not detectable in everyone exposed to the virus. In the study, between 2 to 8.5 per cent of patients did not develop Covid-19 antibodies.

Researchers said this may be because the immune response in these patients could be through other immune response mechanisms, such as different antigens or T-cells. Alternatively, relatively mild infections may be restricted to particular locations in the body, which are not picked up in antibody responses.

The study was led by researchers and clinicians at St George’s, University of London and St George’s University Hospitals NHS Foundation Trust in collaboration with Liverpool School of Tropical Medicine, Mologic Ltd and Institut Pasteur de Dakar, Senegal.

It analysed antibody test results from 177 individuals who had previously been diagnosed with Covid-19.

The pre-print study measured the levels of antibodies in patients exposed to coronavirus. It found that, in those patients with an antibody response, the levels remained stable for the duration of the study – almost two months. Patients with the most severe infections and the largest inflammatory response were more likely to develop antibodies.

This may be due to antibody responses working in parallel with an inflammatory response to severe disease, or that a higher viral load could lead to greater stimulation of the inflammatory and antibody development pathways, researchers suggest.

Sampling by the Office for National Statistics suggests at least 70 per cent of Covid sufferers are asymptomatic. The new findings also suggest such cases are less likely to develop an immune response.

Prof Sanjeev Krishna, corresponding author on the paper from St George’s, University of London, said: “Our results provide an improved understanding of how best to use viral and antibody tests especially when not every person exposed to the virus will have a positive response.

“We need to understand how best to interpret the results … to control the spread of the virus, as well as identifying those who may be immune to the disease.”