The first confirmed case of re-infection of Covid-19 was reported by researchers at the University of Hong Kong in the last week of August. Several other anecdotal cases of re-infection have emerged since then, including here one from Bengaluru.
How exactly is a case of re-infection confirmed? What are the chances of getting infected again after making a full recovery from Covid-19? What does it mean for the long-term immune response to the SARS CoV2 virus which is at the center of the current outbreak?
Scroll.in talked to Dr. Shahid Jameel, a virologist who is the director of the Trivedi School of Biosciences at Ashoka University.
Does positive testing necessarily mean a second time, weeks or months after a first infection and apparently recovering from it, the person is necessarily re-infected?
Reinfection means that you are infected once, you have cleared the infection and then you are infected again.
There may be an anomaly where the virus was very low when you tested negative, and then the next time around it was taken in a test.
Whether it is the same virus that is coming to the surface again or is a case of infection again from another viral event is the question. The only way to test it is to see if the virus the first time and the second time are slightly different.
Viruses, as they multiply in humans, they acquire small mutations. So it is not very likely that a case of re-infection has exactly the same virus, that has exactly the same sequence, about 30,000 nucleotides.
The Hong Kong case is the only good evidence that yes, re-infection has occurred. The first time the person had a virus that had a sequence and in the second infection, the virus had a slightly different sequence.
People really should not run to sequence their virus.
In the case of Bengaluru, I really do not know if they did or did not do the ranking. So I can not say if it really is a case of re-infection.
So you are saying that analyzing the genomic sequence of two specimens from the previous infection and the last infection is the only reliable way to determine a genuine case of re-infection?
Yes. But let me also add that sorting is not something that can be done in a diagnostic lab or in a hospital setting. Requires a special set.
People do not have to really run to sequester their virus. This simply creates unnecessary pressure on the system. I mean, what is at stake here? It’s really theoretical whether someone got infected again or not. What people lack is that the main thing is disease.
We continue to be infected with many viruses that we do not even know about because they do not appear as disease. All this fear of re-infection is premature.
The other thing is, there are over 25 million cases in the world today, and there are these isolated cases of so-called re-infection. It doesn’t matter, basically.
Can you explain the anomaly you referred to earlier, when it is not a case of re-infection, but a person who apparently recovered, after weeks or months, again turns out to be positive? How does this happen?
In such cases of a person being positive in a second case, it may be that what you can detect (in the test) is not a valid virus but viral nucleic acid.
The RT-PCR test (reverse transcript polymerase chain reaction test used to confirm a Covid-19 infection) does not allow you to tell if your sample contains a stable virus that is capable of infecting others or simply contains fragments of viral genetic material without a viable virus. It may be the case that they are simply genomic fragments.
So the genetic material from a dead virus, which remains in the body even after a person has recovered, in this case, the first infection, did the second RT-PCR give a positive result?
Is it correct to say that such people are not able to spread the virus (despite the positive test the second time) and will not themselves suffer from the disease?
What can the Ct value (Cycle Threshold value) tell us as determined in an RT-PCR test? Is there a link between Ct value and disease severity or infectivity?
Much has been done with the value of Ct after Kiran Mazumdar Shaw wrote on Twitter that its Ct value was over 23, so it was not a serious illness. I think she has a very vague understanding of these topics. The absolute value of Ct means nothing. You have to make a comparison.
Let’s say that sample A has a Ct value of 20 and sample B has a Ct value of 30, this simply means that there is more virus in sample A compared to sample B.
Ct means the threshold cycle in which you begin to detect the virus. If you are detecting the virus in a sample after 20 cycles, to begin with, you have more virus in that sample compared to another where you are detecting after 30 cycles. But to say that if someone has 24 cycles or less, they are infectious and that 24 cycles and above are not infectious is unusual. There is no correlation made. This is all conjecture.
You mentioned earlier that viruses acquire small mutations as they multiply in humans. Does the severity of the disease vary with different variants of the virus? Does the clinical response need to be altered in any way for virus variants?
In Covid-19, there is no correlation that a particular variant of the virus causes more severe disease compared to another variant. There is no correlation. As far as we understand, all circulating variants of the SARS CoV2 virus are equally capable of causing disease.
Now, in some people that disease is asymptomatic or mild. In other cases, the disease is moderate or severe. There is no correlation of this with the viral variant. This is how our body reacts to the virus that makes the infection either mild or severe. It is not a property of the viral variant as far as studies done so far show.
Do you see cases of re-infection that have an impact on the effectiveness of possible vaccines?
No. Although the Covid-19 case load worldwide has exceeded 27 million, cases of re-infection are extremely rare.