Emergency paramedics wearing a full COVID-19 coronavirus personal protective equipment (PPE) transfer an empty gurney to an ambulance at the Greenacres Hospital in Port Elizabeth, on July 10, 2020. - Ambulances have to queue before patients suspected of having symptoms related to the COVID-19 coronavirus are triaged and admitted. (Photo by MARCO LONGARI / AFP)
The Covid-19 antibody testing announced by President Cyril Ramaphosa for community-based surveillance will not only gauge if a person had the virus in the past, but could also offer potential clues to how exactly antibodies could fight off the disease.
Dr Shakira Choonara, an independent public health practitioner, has said this would be another tool in our arsenal, needed to learn as much as possible about the virus.
“…there could even be some clues to how antibodies can fight off the virus as they remain in the blood (immunity), but it’s too early to tell. Although, this could be the main reason government is rolling out the antibody tests, to determine if people are ready to return to work or school and if there are any other insights to fighting the disease.
“There needs to be a balance of priorities and targeted efforts given our resource constraints,” Choonara said.
She explained that the new Elecsys Anti-SARS-CoV-2 serology test could support the detection of antibodies against SARS-CoV-2 in patients who have been exposed to the virus which causes Covid-19.
She said detection of these antibodies could help indicate if a person has gained immunity against the virus and inform treatment decisions.
Professor Glenda Davison, head of the biomedical sciences department at Cape Peninsula University of Technology and honorary senior lecturer at University of Cape Town, said antibody or serology tests detect antibodies in the patient’s blood.
After being infected with the virus, our bodies will begin to make antibodies to fight the virus and these usually first appear in the blood around 14 days after first infection and can then be measured using an antibody or serology test.
She said the test works by fixing viral proteins or antigen to a surface and that these proteins are usually a part of the virus such as the spike protein.
Davison explained that the blood is added and will mix with the viral antigen and if the antibodies to the virus are present, they will attach themselves to the protein and can be detected or measured as it will produce a colour.
“I believe that introducing antibody testing is a big step forward as it will assist epidemiologists in knowing the true scale of the infections and also which communities have been affected. We will also learn more about how immunity to the virus is built up and retained after infection. The big disadvantage has been that these tests have up till now not been validated and some of them were shown to be inaccurate. However, I think that SAPHRA (South African Health Products Regulatory Agency) has now validated it and is about to approve the first antibody test in South Africa,” she said.
Dr Atiya Mosam, public health medicine specialist, explained that the difference between the current test and antibody testing was that the current test was an antigen test, which detects the presence of the virus’ genetic information in the host body.
She said antigen tests show that the person is currently infected with Covid-19, while the antibody test detects the body’s response to the virus.
“…the response is usually delayed, so this (antibodies) test can only tell us if someone has been infected at some point which led to the body mounting an immune response. It cannot tell us if the person is currently infected. Therefore we cannot use the antibody test to diagnose active disease, but we can use it to detect how many people in the community or population have been infected,” Mosam explained.
She said this was key as it helps them to understand how many people were theoretically immune because if one has the antibodies, then their body can fight subsequent infections.
“Therefore if we have many people in the community who are immune, then the virus will have less hosts and we will have herd immunity. This will allow us to make decisions about the social measures, for instance the lockdown, opening of businesses and so forth…,” Mosam said.
She, however, noted that there have been cases of people getting infected twice with Covid-19 and that they had no idea how long the antibodies will last and that this meant they would never know how long someone would be immune.
“So this measure is not perfect either. From a practical point of view, an antigen test is one done with a swab of the nasal passages but the antibody test is done using blood. The antibody test will not be replacing the antigen test, so I don’t think it will affect (test results) turnaround times,” Mosam added.
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