While the presence of antibodies against SARS-CoV-2, the coronavirus causing COVID-19, is indicative of past exposure to the virus, it is not synonymous with immunity against it, scientists have clarified.
The clarification comes as serosurveys conducted in the past have led to misconceptions about community-wide immunity.
Scientists say immunity depends on the kind of antibodies, the concentration, and how long they last.
Details: Antibody presence tells us nothing about disease progression: Immunologist
As scientists are trying to understand how antibodies impact the progression of COVID-19, immunologist Satyajit Rath from the National Institute of Immunology (NII) told PTI that antibody presence in itself tells us nothing about disease progression.
Citing scientists, the news agency reported that the only thing the presence of antibodies indicates with certainty is that an individual has been infected in the past.
Antibodies: Different antibodies generated against different parts of viruses
Vineeta Bal from Pune’s IISER told PTI that there are neutralizing antibodies (nAbs) and “simple” antibodies.
Bal said that nAbs block the entry of the virus into a host cell, but there are other antibodies generated against other parts of the virus.
“Simple” antibodies indicate the presence of the virus in the host, but are not helpful in stopping the spread, Bal added.
Quote: ‘Antibody presence doesn’t guarantee protection from disease’
Bal said, “Simple presence of antibodies is a clear indication of previous exposure to SARS-CoV-2 but does not necessarily guarantee protection from the disease in the absence of neutralizing antibodies.”
She added, “Presence of nAbs in sufficient concentrations and for a longer period is the most likely indicator of protection of the individual from next exposure leading to illness i.e. COVID-19.”
Fact: No consensus on nAb levels that could offer immunity
Further, Bal said that there is no consensus on the levels of nAbs in the blood that could offer “protection” against a pathogen. Similarly, the level of nAbs required to ensure that plasma therapy is useful also remains unestablished, she said.
Serosurveys: ‘Antibody tests in market not targeting same viral proteins’
Further, Rath noted, “All antibody tests in the market are not against the same viral protein target, and some investigators use only one target, others use more. And it is possible that tests differ in their sensitivity,” adding that this creates issues with drawing out easy patterns in different serosurveys.
Most serosurveys also report results as simply “positive”/”negative” without analyzing antibody levels, he added.