Eminent epidemiologist and health economist Dr Ramanan Laxminarayan tells Outlook in an exclusive interview why rapid Covid antigen tests are problematic and should not, in any case, replace the existing RT-PCR tests.
While the Delhi government's data on Coronavirus cases shows a decline in the number of positive cases, experts believe that the real picture might not be what it looks like. Eminent epidemiologist Dr Ramanan Laxminarayan, who is also Director of the US-based Center for Disease Dynamics, Economics and Policy, tells Outlook in an interview that it is the testing error which shows Delhi’s Covid-19 situation improving. Excerpts:
Q: Do you think Delhi’s Covid-19 curve is flattening?
There is no real flattening happening in Delhi. It appears to be an artefact to the testing method, ie, antigen test.
Q: So what’s the problem with the antigen test?
It is a less sensitive test. Its sensitivity is reported to be less than 50 per cent. It also appears to be temperature sensitive so if it is hotter, it is less sensitive. Another challenge is that It needs operators’ competence. So the person who is taking the swab should be competent to take the right amount of virus particles from the nasal or throat swab. If he or she doesn't do that, you will not get the right result. It is a very problematic test and it should not replace the RT-PCR test at all.
Q: As you said that it is less sensitive. Does that mean it will give false test report?
It is throwing up a lot of false negatives. False-negative are people who test negative through antigen test and think that they don’t have a virus but actually they are positive and infected. In an antigen test, if you are positive then you are quite likely to have Covid-19 but if you are negative, it is quite likely that you still have Covid-19 and to reconfirm, you have to go for RTPCR test. So if you have to go for RT-PCR test, then why not use the RT-PCR test only.
Q: So what’s the advantage of this test?
The advantage of the antigen test is that it is done as a rapid test and you can get the result in 15 to 20 minutes.
Q: But doesn't the disadvantage outweigh its benefits?
It is quite challenging and I don’t know why the ICMR has pushed this test for Covid-19. The danger is that someone has Covid-19 and you send him off after testing that he doesn’t have Covid. He will not take precautions thinking that he is not infected.
Q: So far as I know, several companies approached the ICMR to get approval for their antigen kit but the medical body has approved only one company, SD Biosensor, which manufactures Standard Q COVID-19 Ag kit. Is it correct?
There is only one antigen testing kit by SD Biosensor which is being used all across the country. I have just come to know from a hospital in Ahemdabad that RT-PCR test has been replaced with Antigen test there. It is a setback to Covid testing quality.