Global data, particularly from South Africa, the UK and the US show that over time as new variants emerge, the one which has better transmissibility and immune evasion takes over the preceding variant.
While the recent surge in Covid cases seen in India is largely due to Omicron, it does not mean that Delta has weakened, experts contended on Tuesday.
India on Tuesday recorded 1,68,063 new Covid cases, taking the total tally to 8,21,446. Although the fresh infections were 6.4 per cent less than Monday when the country logged 1,79,723, the weekly positivity rate has climbed to 8.85 per cent and the daily positivity rate has declined to 10.64 per cent. On the other hand, 4,461 Omicron cases were recorded from 28 states.
So can we say this is an Omicron wave? While it is relatively easy to test for Covid-19 through a RT-PCR or RAT test, figuring out which variant is responsible requires genome sequencing.
Data sent to the open access GISAID genomic surveillance showed that more than 30 per cent of the sequenced samples from India were Omicron during the month of December.
Health experts noted that going by the trend, the majority of the positive cases are likely to be Omicron but confirmation is pending.
“Currently we can sequence only a small fraction of daily cases, so the question is what percentage of those viruses that are sequenced turn out to be Omicron. That’s how we know that we are in an Omicron wave, since most of the sequences have turned out to be those of Omicron,” Gautam I. Menon, Professor at Departments of Physics and Biology, Ashoka University,
Global data, particularly from South Africa, the UK and the US show that over time as new variants emerge, the one which has better transmissibility and immune evasion takes over the preceding variant.
“The same happened with Omicron which is now causing more than 90 per cent of new cases in the US and the UK, India is soon set to follow suit,” Dr Dipu T.S., Associate Professor, Division of Infectious Diseases Amrita Hospital, Kochi.
“This just means that there is a variant with better survival advantage and immune evasion ability compared to the previous variant i.e. Delta. But it doesn’t mean that Delta has become weak, rather it gave way to a better evolved variant in time,” he said.
However, Menon disagreed, saying: “Because Omicron is much more transmissible than Delta, it has effectively displaced Delta while spreading. Delta was largely on the decline in the country anyway, so this was not a surprise.”
Further, the health experts said the surge in cases may also be reinfections, or breakthrough infections as seen in other countries. A recent study showed that the risk of reinfection with Omicron is 5.4 times greater than Delta. So far, nearly all reinfections have been among people who originally caught another strain of the SARS-CoV-2 virus and there is no evidence yet been found of anyone being infected twice by Omicron itself.
It was “too early” for people infected with Omicron to have cleared the virus and then caught it again, Kingston Mills, Professor of Experimental Immunology at Trinity College Dublin, was quoted as saying to Financial Times. It may be clear in six months’ time, he said.
Moreover, the Omicron variant is also known to be able to evade prior immunity. While vaccines can effectively prevent hospitalisation and death due to Covid, they are less effective in preventing infections.
“With luck, the severity of this wave will be less than that of the previous wave, mainly because vaccination levels are high and many were infected in the previous Delta wave. But whether there will be a surge in cases which the health system cannot cope with remains to be seen and this is the main worry at the moment,” Menon said.
Several modelling studies, include from IIT-Kanpur, show that India will soon see a peak in Covid cases by end of January.
“We believe that the peak in cases in the metros of India should come between January 20 and February 10. The rest of India may see later peaks, but it is unlikely that we will continue to see substantial numbers of cases by March. That will mean an end to this wave, but there may be more surprises in store for us,” Menon said.
