Explained: Why Omicron is spreading at such a fast speed despite being mild in most patients

Laboratory studies show the new COVID-19 variant is often limited largely to the upper airway: the nose, throat and windpipe, sparing the lungs, which may be the answer to why it spreads so quickly

FP Staff January 04, 2022 12:44:27 IST
Explained: Why Omicron is spreading at such a fast speed despite being mild in most patients

Representational image. AFP

The world is battling the fast transmitting Omicron variant, with COVID-19 cases reaching record highs.

India, too, is facing a surge of coronavirus infections, with experts saying that metro cities such as Delhi and Mumbai are already witnessing the third wave of the pandemic. In fact, Delhi on Monday reported 4,099 fresh COVID-19 cases and the positivity rate spiralled to 6.46 per cent with Health Minister Satyendar Jain saying the Omicron variant of coronavirus is behind the surge in infections in the city.

In Mumbai, the situation was no different, with the financial capital recording 8,082 cases in 24 hours.

However, one silver lining that can be seen from the new COVID-19 surge is that the hospitalisations are marginally less, with most people being infected asked to home quarantine as their symptoms are mild.

So, does this mean the Omicron variant is less severe? Also, why is that the case? We try to answer these questions.

Omicron less severe

A growing body of evidence is showing that the Omicron COVID variant, first found in South Africa in November, is less severe.

Many studies suggest Omicron carries a reduced risk of being admitted to hospital. In December, two studies based on real-world COVID-19 UK data reported that the Omicron variant is less severe than the Delta variant, with fewer infected people requiring hospitalisation.

Research by Imperial College London found that people with PCR-confirmed Omicron are 40 to 45 percent less likely to spend a night or more in hospital compared with the Delta variant.

Those with Omicron after a previous infection are 50 to 60 percent less likely to be hospitalised, compared with those with no previous infection.

Another research by the University of Edinburgh and other experts in Scotland, based on a small sample of 15 people in hospital, also concluded a two-thirds reduction in the risk of COVID-19 hospitalisation when compared to Delta.
Further data from South Africa suggests people catching COVID-19 are 80 percent less likely to be taken to hospital with Omicron, compared with other strains.

Why is Omicron considered less serious?

Six studies — four published since Christmas Eve — have found that Omicron does not damage people’s lungs as much as the Delta and other previous variants of coronavirus.

However, these studies have yet to be peer-reviewed by other scientists.

Deenan Pillay, professor of virology at University College London, explaining to The Guardian, said, “In essence, it looks to be more able to infect the upper respiratory tract – cells in the throat. So it would multiply in cells there more readily than in cells deep in the lung. This is really preliminary but the studies point in the same direction.”

A team of researchers at Hong Kong University’s faculty of medicine found that the Omicron variant was much quicker at getting into the bronchus or tubes that run through the upper airways and lungs but much slower at infiltrating the lung tissue itself.

According to the researchers, the Omicron variant replicated less efficiently, more than 10 times lower, once inside the human lung tissue than the original SARS-CoV-2 virus, which may suggest lower severity of disease.

Last week, a group of American and Japanese scientists released a report on hamsters and mice that were infected with the Omicron variant or earlier coronavirus strains. Those infected with Omicron had less lung damage and were less likely to die. The researchers noted that Syrian hamsters, which have become severely ill with previous versions of the coronavirus, also had milder symptoms.

A team in Glasgow think they have found the answer as to why this variant is unable to infect the lung cells as much as it does the upper airways.

According to their research, a protein found on lung cells — called TMPRSS2 — which usually helped previous SARS-COV-2 variants to gain entry into the lung cells themselves bound less strongly to Omicron. This is why, according to them, the new variant finds it tough to get inside and infect lung cells.

This also could be the answer to why Omicron is more transmissible. As it is concentrated in high quantities in the upper airways, it is more likely to be coughed, sneezed or breathed out from these parts of the airways and infect other people.

With inputs from agencies

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