Study finds antibodies target different parts of SARS-CoV-2 in severe COVID-19 cases

The body’s protective antibodies against the novel coronavirus target a different part of the virus in severe cases of COVID-19 than they do in mild forms of the disease, and wane significantly within several months of infection, a new study says.

According to the scientists, including those from Stanford University in the US, the findings shed new light on the links between the course of the disease and a patient’s immune response.

The research, published in the journal Science Immunology, found that people with severe COVID-19 have lower levels of antibodies targeting the spike protein used by the virus to enter human cells than those targeting proteins of the inner shell of the SARS-CoV-2 virus.

“This is one of the most comprehensive studies to date of the antibody immune response to SARS-CoV-2 in people across the entire spectrum of disease severity, from asymptomatic to fatal,” said Scott Boyd, co-author of the study from Stanford University.

In the study, the scientists studied 254 people with asymptomatic, mild or severe COVID-19 who were identified either through routine testing or occupational health screening at Stanford Health Care or who came to a Stanford Health Care clinic with symptoms of COVID-19.

According to the scientists, 25 of the people with symptoms were treated as outpatients, 42 were hospitalised outside the intensive care unit and 37 were treated in the intensive care unit.

The study noted that 25 people in the study died of the disease.

From the analysis of patient samples, the scientists said antibodies that recognise and bind to the spike protein prevent the virus from infecting the cells.

However, they said the antibodies which recognise other viral components are unlikely to prevent viral spread.

The researchers assessed the levels of three types of antibodies — IgG, IgM and IgA — in the patients.

They estimated the proportions of antibodies which targeted the viral spike protein or the virus’ inner shell as the disease progressed and patients either recovered or grew sicker.

“Those people with mild illness tended to have a higher proportion of anti-spike antibodies, and those who died from their disease had more antibodies that recognised other parts of the virus,” he added.

While the study identified trends among a group of patients, the scientists said there is still substantial variability in the immune response mounted by individual patients, particularly those with severe disease.

They believe antibody responses are not likely to be the sole determinant of someone’s outcome.

The scientists also found that people with asymptomatic and mild illness had lower levels of antibodies overall than did those with severe disease.

Levels of IgM and IgA decreased steadily in patients post-recovery to low or undetectable levels over a period of about one to four months after symptom onset, and IgG levels dropped significantly.