Scientists document cases of asymptomatic reinfection

September 16, 2020 12:00 am | Updated 05:24 am IST - NEW DELHI

Report says this may be a ‘potentially under-reported entity’

Under the scanner:A worker checking the temperature of a differently-abled child at a home in Mumbai.Emmanual YoginiEmmanual Yogini

Under the scanner:A worker checking the temperature of a differently-abled child at a home in Mumbai.Emmanual YoginiEmmanual Yogini

Researchers have reported what may possibly be the first instance of people in India being infected twice over by SARS-CoV-2 but remaining asymptomatic. Moreover, one of those infected appeared to carry a variant that conferred resistance to neutralising antibodies.

The report appears in a paper that has been posted on a pre-print repository, meaning it has not been peer-reviewed.

Globally and in India, there have been intermittent reports of people being infected at least twice and confirmed positive by an RT-PCR (reverse transcription-polymerase chain reaction) test. However, they have almost always involved the person being symptomatic at least once.

“Our analysis suggests that asymptomatic reinfection may be a potentially under-reported entity,” say the authors of the report that include a team of doctors and geneticists from the CSIR-Institute of Genomics and Integrative Biology (CSIR-IGIB).

Healthcare workers

The people who tested positive are healthcare workers at the Government Institute of Medical Science, Greater Noida, Uttar Pradesh, and their infections were picked up as part of routine surveillance that the hospital conducts on its staff.

The fact that the patients were infected twice could be reliably established because the viral samples gleaned from their nasal swabs underwent a whole-genome sequencing. This ruled out potential instances of their lab samples being contaminated or a false positive, or an old infection getting reactivated.

The healthcare workers first tested positive on May 5 and May 17 respectively, and were hospitalised according to the hospital policy even though they were asymptomatic. They tested negative on May 13 and 27 respectively. After they resumed work, they again tested positive on August 21 and September 5 respectively. They were home quarantined, and tested negative again 14 and six days later respectively. “Both individuals were asymptomatic but had a higher viral load in the second episode of reinfection,” the authors note.

“This was posted as a research communication because we need to let people know of the chances of reinfection, particularly among healthcare workers, and thereby a need for greater surveillance,” said Sridhar Sivasubbu, scientist at CSIR-IGIB and one of the co-authors of the paper.

With increased access to RT-PCR testing and the virus having spread to every corner of the country, reports of reinfection are increasing. “There are reports of four cases in Mumbai, at least one in Delhi. The number of cases [of possible reinfection] where the IGIB is involved, but we haven’t finished the genome sequences, are 16. There are several more research studies forthcoming where we have reported reinfections,” said Anurag Agrawal, Director, IGIB. To establish such reinfections beyond doubt, the virus samples from both episodes were required and of the 16, the IGIB only had 9 samples from both episodes, said Dr. Agrawal.

“It is noteworthy that a genetic variant 22882T during reinfection in [one of the patients] possibly confers resistance to neutralising antibodies,” the authors note.

Neutralising antibodies are a type of antibody that binds to viral particles and prevents them from infiltrating the body’s cells.

Earliest case

The earliest case of confirmed reinfection emerged from Hong Kong, where a person first tested positive in March and then was found positive again after an airport screening in August, according to a report in Clinical Infectious Disease , published by the Oxford University Press. This, too, was confirmed by genomic sequencing.

At a press briefing on Tuesday, Dr. Balram Bhargava, Director General, Indian Council of Medical Research, said, “Reinfection is very rare with COVID-19. What has been observed so far is that whenever this occurs, both infections have been very mild. So it is not really a serious concern now”.

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