PCR tests not completely infallible - Immunologist

Head of Advancement at the West African Center for Cell Biology of Infectious Pathogens (WACCBIP) Dr. Yaw Bediako, has stated that Polymerase Chain Reaction(PCR) tests are not completely infallible, as one can test positive on the antigen test and also test negative on the PCR test depending on where they are on the spectrum of the infection.

He said this in an interview with Alfred Ocansey on 3FM’s Sunrise morning show on Thursday, April 29.

Dr. Bediako was speaking on the back of travelers testing negative from their country of origin but testing positive on arrival, thus surging Ghana’s positive cases in recent times.

He said “it’s actually not difficult for this to happen and it actually does not necessarily mean the airport test is not working, when you come in there’s a 72 hour window between when you have taken a PCR test and when you are taking the antigen test at our airport. And also, obviously after you take the PCR test, a lot can change between then and when you take a subsequent PCR test, PCR tests are not completely infallible, over time, over the course of the infection, you are less positive in your throat as the virus moves further down into your respiratory tract.

“So it is possible for someone to show up at the airport, test positive on the antigen test but then subsequently, perhaps test negative depending on where they are in the spectrum of the infection. So, of course you could ask if there was something that went wrong at any of these testing places, either at the airport or at the hospital but certainly even if both of these tests are working optimally, we could potentially still have had this situation where somebody in the interval, between when they tested positive would then convert to negative, as it were by PCR”.

He further stated that “yes, I mean these cases are relatively rare but they can happen, you know none of these tests are 100% full proof, so every once in a while something like this can happen, which is why typically, you would want to have a confirmatory test. You know as this gentleman has now tested negative, I think the thing to do is to have a final follow up test to see what his current status is, because it is possible he was negative when he arrived but once he took the next PCR, that point he was testing negative. This is the importance of testing, you have to test, you know if you keep testing you will have the assurance that you are catching most of the cases but I don’t think that there is any reason to suspect foul play necessarily, this is a possible scenario it could happen with existing testing”.

When asked about his reaction to Ghana’s bid to go for Russia’s Sputnik V vaccine due to the lack of availability from India because of their dire COVID-19 situation, he replied that “for me, I think it raises serious questions about Sputnik V, the data that has been released by Reuters and has been picked up by other biological institutes, basically some tests in Brazil have revealed that the vaccine itself may not have been manufactured properly, to put it in simple terms and so the Brazilian government have rejected it, I know the vaccine is currently under review with the European Medical Agency.

“And in my opinion, I think, given what has happened in Brazil, Ghana will be prudent to wait for the report from the European Medical Agency before we decide what to do, I mean with the emergency use authorizations we have done, it has been based upon the reports, for AstraZeneca it was based upon the WHO reports and I think for Sputnik, at this point it is based on fewer kind of regulatory processes, given what has happened in Brazil, it’s probably a good idea for us to wait for the European study to come out before we decide to use it, because what it essentially suggest is that the vaccine will not be as safe as it should be”.