Catching Covid again? Jury is still out
Rigorous studies have to be conducted before scientists can determine if Covid-19 reinfections occur.
That’s according to the chair of the Covid-19 ministerial advisory committee, Professor Salim Abdool Karim.
A Durban doctor, however, said some of his patients showed positive results for the coronavirus more than once.
Dr Yuvan Maharaj told the Sunday Times he was being confronted by a “barrage of patients who are retesting either true or falsely positive after three months. My reasons for raising this issue is that the quality/efficacy of testing and analysis needs to questioned,” he said.
“Are we seeing a whole cluster of falsely negative people walking out there? I think it’s relevant and should be questioned.”
Karim said: “There have been sporadic cases. They come from South Korea, China and so on where patients test positive on a PCR [a diagnostic test], then test negative and then test positive later on.”
These, he said, have been ascribed to reinfection.
“The PCR only tests for the RNA [genetic material] of the virus. It does not test for whether there is actual virus there and whether that virus is alive or not.”
Three recent studies showed that the virus is only alive for about seven to eight days after a patient shows symptoms.
“After that you can still test positive on the PCR … but there is no infectious virus.
“When you see somebody test positive then negative and positive again, you should not draw the conclusion that this person got the virus, recovered and got infected again. The chance that it’s true is quite small,” said Karim.
“The problem with what the doctor has observed is that it’s not done as a rigorous study, where we can go look at the data, ensure the viruses are different, make sure the antibodies have come up, make sure that this new virus was able to escape the antibodies.”
Karim believes China would be the most apt setting for such a study because the virus presented itself there first.
“In Wuhan, if they get another virus spreading, we will be able to answer the question [about reinfection].
“In SA we would have to wait a bit longer. We will be able to answer that question probably later this year.”
Karim said that at this stage “we just don’t know the answer”.
Dr Jantjie Taljaard, an infectious disease specialist at Tygerberg Hospital and head of the division of infectious diseases at Stellenbosch University’s faculty of medicine & health sciences, believes the uncertainty around reinfection “is created by a poor understanding of how a PCR test works as well as an incomplete understanding of how immunity to viral infections work. And, of course, the fact that the scientific community has only had six months to try and figure out how this novel virus can be diagnosed, treated and prevented.
He said: “Most of the case reports of potential reinfection are based on the PCR test becoming negative and then later positive again.
“A positive test within three months after Covid-19 is most likely due to fragments of genetic material still hanging around in the respiratory tract and is not an indication of active disease.”
Taljaard said a negative result between two positives might be the result of poor technique or low viral load at the time.
“It is likely that at least short-term immunity [for at least three months] against reinfection occurs in most people who recover from Covid-19.
“It is as yet unknown but possible or even likely that some level of immunity may persist for longer.”