Scientists from St. George's University of London in the UK said antibodies were not detectable in everyone exposed to the virus, opening discussions on how best to interpret antibody and viral tests.
The yet to be peer-reviewed study, published in the preprint repository medRxiv, sheds light on the duration for which people remain immune after contracting COVID-19, and provides insight into how different age and ethnic groups respond to infection.
In the research, the scientists analysed the antibody test results from 177 individuals diagnosed with COVID-19, and measured the levels of antibodies against the novel coronavirus they had.
According to the scientists, in patients with an antibody response, the levels of the immune molecules remained stable for the duration of the study (almost two months).
Based on the study, the researchers said patients with the most severe infections who have the largest inflammatory response were more likely to develop antibodies.
They hypothesised that this may be due to antibody responses working in parallel with an inflammatory response to severe disease.
The scientists said a higher viral load may also lead to greater stimulation of the inflammatory and antibody development pathways.
However, the researchers cautioned that further work is required to understand if and why this may be the case.
Between 2 and 8.5 per cent of patients did not develop COVID-19 antibodies at all, they added.
According to the scientists, this may be because the body's defence response in these patients could be through other mechanisms like the immune system's T-cells.
Another option, they said, could be that relatively mild infections may be restricted to particular locations in the body, such as within mucosal cells of the respiratory tract, where antibody responses are dominated by a secretory immune system.
The scientists also assessed the associations between different characteristics and antibody responses.
They said older patients and those with other conditions, such as with hypertension and being overweight were also more likely to have an antibody response.
"Our results provide an improved understanding of how best to use viral and antibody tests for coronavirus, especially when not every person exposed to the virus will have a positive response," said Sanjeev Krishna, co-author of the study from St George's, University of London.
Krishna believes that interpreting the results from these tests can help in controlling the spread of the virus, as well as identifying those who may be immune to the disease.
"We hope that by sharing our data at an early stage, this will accelerate progress towards effective use of test results around the world," he added. VIS VIS