Covid-19: What you need to know today

The fact that most early antigen tests for Covid-19 were unreliable was worrying, but expected. Most people) were convinced that the problem was a temporary one.
Antigen tests have been around for some time. They have always been relatively inexpensive. And they have always been quick.(AFP)
Antigen tests have been around for some time. They have always been relatively inexpensive. And they have always been quick.(AFP)
Updated on Aug 29, 2020 02:14 AM IST
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Hindustan Times, New Delhi | By

This isn’t a plug for Abbott Laboratories as much as it is recognition of what the company’s new antigen test — $5, 15 minutes, simple, and highly accurate — represents at a generic level, for it is certain to be the first of many similar tests that all promise the same things. Low cost. High accuracy. Fast results. The very fact that I am celebrating these reflects what we have had to live with for the past eight months of the coronavirus disease. Tests that are complex (either in terms of testing requirements or expertise). Tests that are slow. And tests that are inaccurate. Those are the kind of trade-offs even people who understand testing have had to make. As for those that don’t, one test is as good as another — a behaviour exemplified by the Union health ministry and the Indian Council of Medical Research (ICMR), both of whom should know better, not bothering to enforce, or even issue guidelines on when which kind of test should be used.

Antigen tests have been around for some time. They have always been relatively inexpensive. And they have always been quick. But they were also inaccurate when it came to so-called false negatives, or showing infected people as uninfected. This low specificity (the technical term for what are called true negatives, which means someone identified as uninfected in the test is actually uninfected) made them unreliable. Around the world, researchers, health care workers, and policymakers insisted that the right way to use them (if they had to be used) was to follow up a negative test with another antigen test or, preferably, a molecular test such as the Reverse Transcription Polymerase Chain Reaction, or RT-PCR, one.

Where time is a constraint, the use of antigen tests makes sense. For instance, they can help isolate infected people quickly in containment zones, or hot spots of the virus. Where it isn’t, molecular tests must be used.

The fact that most early antigen tests for Covid-19 were unreliable was worrying, but expected. Most people (including this writer) were convinced that the problem was a temporary one.

Science (and Big Pharma) were sure to find an answer to this — testing is an area where we have made huge progress over the years. Ergo, it was only a matter of time before companies started launching accurate antigen tests. We now have one. And there is a very high likelihood that there will be many more. We may even have molecular tests that provide results within the hour.

According to clinical studies, the specificity and sensitivity (ability to identify true positives, or an infected person as infected) of the Abbott antigen test is on par with that of molecular tests such as RT-PCR. For those interested in details, the Abbott test’s sensitivity is 97.1% and specificity 98.5%. That’s a big jump over the previous generation of antigen tests.

There is a caveat, though: field performance of any test, even the RT-PCR one, rarely matches its clinical performance. There have been some high-profile instances of RT-PCR tests going wrong (and that is only to be expected; that some of these will go wrong is a mathematical possibility).

Still, the new antigen test (currently launched only for the US), and those that will invariably follow, provide a near-perfect solution to testing. And by providing accurate results soon (the antigen tests being used in India provide results within the hour, but are not very accurate) they can help isolate infected people, regulate entry into offices, schools and colleges, public places, and public events – basically play a key role in the return to normalcy.

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  • ABOUT THE AUTHOR

    Sukumar Ranganathan is the Editor-in-Chief of Hindustan Times. He is also a comic-book freak and an amateur birder.

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