April 18, 2020 14:01:30
The World Health Organisation (WHO) is not sure whether the presence of antibodies in blood gives full protection against reinfection with the new coronavirus.
- Countries, including Australia, are rolling out antibody testing for COVID-19
- But the WHO says there is no evidence these tests show that those tested are immune or protected from reinfection
- It says there is little evidence of “herd immunity”, where large numbers of people had developed antibodies
Experts from the organisation said it currently has no evidence that antibody tests can show that an individual is immune or protected from reinfection with COVID-19, despite a number of countries proposing to roll out such testing to measure immunity.
These finger-prick tests, officially known as serologic tests, analyse serum or plasma for evidence of antibodies generated to fight off COVID-19. They do not detect the virus itself.
Antibodies are proteins that can stick to the surface of, and fight off, viruses or bacteria.
WHO emergencies expert Mike Ryan said the organisation does not have a position on the use of serologic testing and urged countries to be careful about relying on the results to measure immunity.
“There’s lots of uncertainty around what such a test would be and how effective and how performant that test would need to be,” Dr Ryan said.
“We also need to look at the length of protection that antibodies might give nobody is sure whether someone with antibodies is fully protected against having the disease or being exposed again.
“Plus, some of the tests have issues of sensitivity. They may give a false negative result and we may actually have someone who believes they’re serial positive and protected actually in a situation where they are exposed and they are susceptible to the disease.”
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Dr Ryan also said that even if antibodies were effective, there was little sign that large numbers of people had developed them after contracting coronavirus and were offering so-called “herd immunity” to the broader population.
If herd immunity does not develop, governments around the world face the possibility that the virus may spread again once social-distancing measures are lifted.
“A lot of preliminary information that’s coming to us right now would suggest that quite a low proportion of the population have actually seroconverted [to produce antibodies],” he said.
“There’s been an expectation maybe that herd immunity may have been achieved and that the majority of people in society may have already have developed antibodies I think the general evidence is pointing against that and pointing towards a much lower serial prevalence, so it may not stop the problem that governments are trying to solve.”
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Technical lead of the WHO’s COVID-19 response Maria van Kerkhove said it was a positive development that so many tests for the virus had been introduced into the market, but it was important these tests be validated to ensure they measured what they were attempting to measure.
She said serologic tests measure the level of antibodies “and it’s a response that the body has a week or two later after they’ve been infected with this virus”.
“But that does not mean that somebody with antibodies [is] immune.”
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The Health Department confirmed at the end of March that antibody tests would soon be deployed in Australia and the Therapeutic Goods Administration (TGA) has approved several serology-based testing kits for COVID-19.
But the TGA has specifically warned the Australian public against buying these tests themselves and using them for self-testing.
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