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ICMR cut-off for Covid reinfection arbitrary, could lead to missed cases, experts say

Virologists and epidemiologists say instead of just using arbitrary cut-off, it is better to use technology to ascertain whether it is a case of Covid reinfection.

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New Delhi: The Indian Council of Medical Research’s (ICMR) announcement of a 100-day cut-off criteria to identify cases of Covid-19 reinfection has been termed as “arbitrary” by experts.

ICMR Director General Balram Bhargava had said earlier this week that “we are taking 100 as the cut-off period because the antibodies last until then”.

Bhargava’s remarks came a few days after Union Health Minister Harsh Vardhan said some of the supposed cases of Covid reinfections that had been reported were misclassified.

The virologists and epidemiologists who ThePrint spoke to on the matter, however, pointed out the ICMR’s criteria is only based on the “assumed life of antibodies (cells that fight the virus)”, and that it might lead to missing out on many cases because of a fixed cut-off.

“In some people, it (antibodies) may be faster and in others it may take longer. Therefore, instead of just using an arbitrary day cut-off, it is better to use technology to ascertain whether it is a case of reinfection,” noted virologist Dr Shahid Jameel told ThePrint. 

The experts, however, added this won’t have any drastic impact on public health response to Covid.

ICMR spokesperson Dr Rajnikant Srivastava said reinfections depend on several factors. 

“If you are infected but you don’t develop the antibody, you may get reinfection. But if you are developing the antibody against Covid, that might protect you during the second infection. So how can you measure whether antibodies are there or not?”

Srivastava said since there are not too many reinfections, the ICMR has not planned a study to look into the genomic differences.

Also read: Modi govt admits Covid reinfections are happening, but says infection mild both times

Looking back

Worldwide, the first case of reinfection was reported in Hong Kong in August, four and half months after the patient’s first bout.

Earlier this week, The Lancet Infectious Diseases reported the first confirmed case in the US in which a 25-year-old man contracted the virus, nearly 50 days after recovering from the first infection. 

Prior to ICMR’s Tuesday press briefing, India had reported only a handful cases of “reinfections”. This included two cases in Telangana in August and four in Mumbai last month.

According to the ICMR’s cut-off limit, only three cases — two in Mumbai and one in Hyderabad — can be classified as cases of Covid reinfection.

On 15 September, researchers from the Institute of Genomics and Integrative Biology in New Delhi uploaded the pre-print of a paper confirming the reinfection of two healthcare workers in Noida

In most of these cases of reinfections, the gap ranged from anywhere between 19 days and over 100 days. 

In August, Fortis Hospital in Bengaluru had witnessed a case of reinfection. The patient, a 27-year-old woman, was first admitted to the hospital on 6 July after testing positive. She was discharged on 24 July after testing negative. 

But in the last week of August, the woman once again developed mild symptoms and tested positive, which is less than the ICMR’s 100-day cut-off limit.

Dr Pratik Patil, a consultant of the Infectious Diseases at the hospital, said: “The ICMR’s cut-off of 100 days is arbitrary and based on studies that suggested once one develops antibodies after Covid infection, they stay for nearly 3 months.” 

However, he added, this is average and it can vary in both directions.

In June, a study published in Nature Medicine had found that antibodies from Covid-19 only last two to three months. 

When asked about the patient who had tested positive for a second time, Patil said the CT or Cycle Threshold value, which is the number of cycles it takes for the RT-PCR device to detect the novel coronavirus, won’t be low in the second time.

“There can be an argument that it could be viral debris after initial infection, but usually in that case, the CT value won’t be so low after 52 days (time between first and second RT-PCR tests). So reinfection is the best possible clinical explanation,” he added. 

In a similar case in July, a Delhi policeman had also tested positive for the second time, within 45 days of recovering from the first bout of infection. 

Dr Rajesh Chawla, a senior consultant of respiratory and critical care medicine at Apollo Hospitals, who was treating the policeman, said: “While there were symptoms the first time, there weren’t any symptoms the second time.” 

On the ICMR’s 100-day limit, he said: “It is slightly tricky as going by the symptoms, it was a case of reinfection but of course the gap was lesser than 100 days in this case.”

Also read: Study documents 2 cases of reinfections in India, but experts say data doesn’t offer insight

‘Sequence the virus the first and second time’

At the heart of the debate is the issue of distinguishing between the leftover viral debris from the initial infection and the new infection. RT-PCR tests cannot draw a distinction between the two. 

Jameel said: “The only confirmed way to ascertain reinfection is to sequence the virus the first and second time.”

Explaining the immune reaction to viruses, T. Jacob John, a senior virologist and former professor at the Christian Medical College in Vellore, said, “The robust sterilising immunity takes anywhere between two to four weeks…”

He added: “If you double it, it becomes 50 days. Beyond that, it is not reasonable to think that your immunity is not robust enough. So if you see somebody infected after 50 days, it should be reinfection, 100 days is an extremely conservation measure.”

John described the ICMR’s criteria as a “sociological answer to a scientific question” where the exact answer is not known, and is being implemented to avoid panic among people.  

‘No great impact’

The experts, however, said that the “arbitrary” cut-off limit will not gravely impact public health response to Covid. 

Highlighting that cases of reinfection are still rare, Jameel said, “Of about 38.5 million confirmed infections globally, there are only just a handful of re-infection cases.”

He added: “Infection does not mean disease. Even if antibodies wane off and someone gets re-infected, T cell immunity would protect from the disease for this virus. And that’s how most vaccines also work — they don’t prevent infection, but attenuate disease.”

John said there is no cause for worry if there are no symptoms the second time and the virus does not “invade” deeply. 

“Now how many diseases do people look for the second infection? Here we are finding a phenomenon which I think is a real phenomenon but it is a rare phenomenon,” he added.

Fortis Hospital’s Patil, however, raised concern. 

“We may miss out on many cases just because there is a fixed cut-off. I think each case should be assessed based on clinical data since it is a new disease and we still don’t know many things.”

Lalit Kant, the former head of epidemiology and communicable diseases at the ICMR, also said: “If a person is harbouring the same infection inside the body, then we need to develop the parameters to know that.” 

(With Inputs from Aneesha Bedi)

Also read: Why a Covid vaccine can provide better immunity than an actual infection


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