December 5: What we know about Omicron variant so far

The number of Omicron cases and their share in genotyped samples has consistently risen across several parts of the world over the weekend.

The first two cases in India were confirmed on Thursday and by Sunday, the tally grew to 21. In South Africa, where the variant is believed to have taken hold in some regions, the weekly average of new infections jumped from less than 2,000 on November 28 to over 8,500 on December 4. In the UK, Omicron’s share in all samples analysed to determine their genome sequence roughly doubled every three days. Similar growth has been recorded in European genome surveillance.

To be sure, some of these trends may reflect a bias – countries are now targeting testing at people suspected to have the variant (due to their travel and contact history) and are genotyping more samples. But they fit into a consistent trend seen since the beginning of the month from several parts of the world, reinforcing the assumption that the variant is significantly more transmissible.

Reduced incubation?

On Sunday, a press release by the UK government announcing mandatory pre-departure test for anyone wanting to enter the country cited new analysis by the UK Health Security Agency (UKHSA) that indicates “the window between infection and infectiousness may be shorter for the Omicron variant”.

There are two ways to look at this: first, it strengthens the assumption that the large number of mutations in Omicron is causing changes in how Covid-19 could clinically manifest.

Second, as the UK government noted, a reduced incubation period increases the likelihood that pre-departure tests will identify positive cases before travel.

The UKHSA cited is yet to be released.

Milder infections?

Experts are watching local disclosures from hospitals in South Africa’s Tshwane, which is in the Gauteng province – the hotspot of Omicron infections. The university hospital in Pretoria released a patient snapshot of the district hospital in Tshwane, where about 21% of the patients were on oxygen support after developing Covid-19.

The assessment adds: “This is a picture that has not been seen in previous waves. In the beginning of all three previous waves and throughout the course of these waves, there has always only been a sprinkling of patients on room air in the COVID ward”.

The report, thus, implies that there are more Covid-19 patients in regular wards of the hospital than on oxygen support compared to previous Covid-19 waves which were caused by other variants.

While this could be good news, there are several factors that could be involved – most of the infections may have happened in younger people, who are more likely to have high contacts. But, more importantly, it could simply be too soon for the infections to have progressed to a stage where people need oxygen support.

The larger threat

The question over whether the variant causes more severe disease is one of two that scientists are racing to answer (that it has high transmissibility is all but confirmed) -- the other is how resistant is it?

A recent mathematical modelling has shown that variants with higher transmissibility are bad in themselves, but they become significantly worse if they are resistant to antibodies (from past infection or vaccines).

Published in the journal Cell, the study by researchers from Harvard said: “Variants with enhanced transmissibility frequently increase epidemic severity, whereas those with partial immune escape either fail to spread widely, or primarily cause reinfections and breakthrough infections”.

But if a variant has both the traits – high transmissibility as well as the ability to escape immunity – “a variant can continue spreading even as immunity builds up in the population, limiting the impact of vaccination and exacerbating the epidemic.”

Last week, a preliminary scientific assessment from South Africa said the variant appeared to be significantly more resistant to natural immunity in people who previously had Covid-19. They were yet to study the effects on those who had a vaccine, or both, a shot and an infection.

The UKHSA, in a report released on Friday, said structural modelling by University of Oxford made similar conclusions.

The wait for conclusive evidence on this, however, continues.

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