Ten regional labs will genetically sequence all positive samples — via RT-PCR — that have had a cycle threshold (CT) value of 30 or less. The CT value is the number of cycles an RT-PCR device has had to run to amplify viral RNA for it to reach detectable levels. A CT value of 30 or less indicates high viral load in the infected person’s throat/nasal swab samples.
The central surveillance unit (CSU) has been asked to ensure adequate representation of such randomly selected positive samples, particularly from metro cities that may have seen a high number of incoming international passengers.
“If the UK variant, or any other serious mutation, is detected in a sample, it will be sent to either one of the two notified Covid Virus Repositories (CVR) — at RCB Faridabad or NIV Pune — for isolating of the virus and further culturing,” a senior Indian Council of Medical Research (ICMR) official said.
The official added the process would help in the development of improved diagnostic tests that could validate the efficacy of current testing methods and vaccines.
But data from the genome sequencing labs will also be used to track infection trends, which could determine if new variants have caused surges in the community. “This data will help us understand super-spreader events and outbreaks. The information will strengthen public health interventions across the country,” said another top official.
Scientist Raman Gangakhedkar, former head of ICMR’s epidemiology and communicable diseases division, explained why the focus is on high viral loads. “Samples will need a high viral load because they will be analysed again during genome sequencing. This is because some portion (viral particles) will get used up in the first test with the RT-PCR.”
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