Whether reinfection cases existed at a population level or the Hong Kong case was an exception had to be studied, WHO said
Conversations regarding reinfection of SARS-CoV-2 have been around for quite some time now but the University of Hong Kong (HKU) has done the first genome sequence for such a case.
The sequencing revealed that the virus strain of the second episode of the infection was clearly different from first one, thus confirming that it was a case of reinfection.
The illness caused due to reinfection, that happened 4.5 months after the first episode, was however mild. This may indicate either of the two following scenarios. Some amount of antibodies to fight the virus were actually after the first episode but were not good enough to fight off completely and hence the virus could not be kept at bay. Or, it may indicate that for the second time, the exposure to the virus itself was less so it caused mild illness.
Genome sequencing for such a case was a first, the researchers claimed. “Viral genomes from the first and second episodes (of infection) belong to different clades / lineages. As many as 24 nucleotides were different between the viruses found in the first and the second episodes,” a press release issued by HKU, said.
What does this ‘difference’ indicate? It was not the same virus surviving in the body that caused the first and the second episodes.
Had the same virus strain remained in the body, the difference would have happened in say, just one or two nucleotides. This would have happened because the person never got cleared of the virus in the first episode itself.
“But if the difference has happened in 24 nucleotides of the virus strains, it means the person cleared the virus at the first instance. And then, s / he got the virus again from the second source. This proves the reinfection,” T Jacob John, former professor of virology at Christian Medical College, Vellore said.
John, however, explained that the reinfection might happen due to a number of reasons, including minor immunodeficiency. “This seems a rare case. If reinfection was common enough, it would have been picked up at many places,” he added.
When this question was raised in the World Health Organization (WHO) press conference on August 24, Maria Van Kerkhove, the technical lead at WHO, said it was not immediately known if the person concerned had developed neutralising antibodies.
Neutralising antibodies are the ones that fight against the virus. Kerkhove said even if this was the first documented case of reinfection, one should not jump to any conclusion and rather look at whether such cases existed at a population level or if it was an exception, as John also suggested.
She said from the experience with other coronaviruses like Severe Acute Respiratory Syndrome and Middle East Respiratory Syndrome, it was known that that reinfection was a possibility.
But to say so about SARS-CoV-2, one should wait for results from studies that were tracking the same population overtime across various settings to study what the nature of antibody response was — whether it lasted for long or did not.
Jury out on Indian serosurveys
Last week, the WHO said a few of Indian serosurveys had shown exceptionally high levels of seropositivity, referring to the one done in Mumbai.
The serosurvey conducted by the Tata Institute of Fundamental Research for the Brihanmumbai Municipal Corporation had said as many as 57 per cent of the slum population of three wards and 16 per cent of the non-slum population had shown prevalence of antibodies.
Therefore, WHO had asked the Indian researchers to make a presentation before it. “We are still working to look at which Indian surveys have looked at neutralising antibodies because these are quite important to us,” Kerkhove said.
So far none of the serosurveys conducted in India have actually measured the proportion of neutralising antibodies. The faculty member of Indian Institute of Science Education and Research, who conducted the serostudy in Pune had told Down To Earth last week that they were studying this precisely as follow-up exercise.
The seropositivity in the wards of Pune that were surveyed was found to be 51 per cent.
WHO chief scientist Soumya Swaminathan also spoke on the US emergency authorisation to convalescent plasma as therapy for COVID-19.
She said while it was up to countries to give such an urgent permission, none of the studies examined by WHO had been conclusive about the efficacy of this therapy. It was still very much at an experimental stage. India, incidentally, had also given an emergency authorisation for it.
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