A new five-month longitudinal analysis of Covid-19 patients who displayed a wide range of disease severity – from asymptomatic to deadly illness – suggests that IgA and IgM antibodies to the SARS-CoV-2 virus disappear quickly during convalescence.
IgG antibodies likely persist for longer, but the research team from the Stanford University in the US, documented a slow, inexorable decline in this antibody class as well, even in severely ill patients who mounted very strong initial antibody responses.
For the study, published in the journal Science Immunology, the research team studied 983 plasma samples collected up to five months post-infection from 79 hospitalised Covid-19 patients and 175 outpatients and asymptomatic people infected with SARS-CoV-2.
The researchers found a higher ratio of antibodies that react to the viral spike protein complex (versus those that target the nucleocapsid protein) in patients with mild illness compared with the severely ill patients, suggesting that this preponderance of spike-reactive antibodies may have helped to blunt the severity of symptoms.
To facilitate their work, they also developed an immunoassay that can detect successful blocking of the viral receptor-binding domain’s interaction with the human ACE2 receptor in human samples, providing an effective surrogate for detecting neutralizing antibodies.
The authors said their findings may raise important questions about the reliability of seroprevalence studies, since the rapid waning of antibody titters may lead to an underestimation of how many people may have been previously infected in a given population.
“The decrease in antibodies after infection also raises the question of how long antibodies elicited by vaccination will last, and whether frequent boosting will be needed to maintain protection,” the authors noted.
Recently, a study published in the Journal of Infectious Diseases in November, revealed that the vast majority of individuals have detectable antibodies up to three months post contracting Covid-19 virus.