December 9: What we know about Omicron today

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New Delhi: The first scientific studies have now almost unanimously confirmed that the Omicron variant is significantly more resistant to immunity elicited by vaccines and past infection. The variant was designated as being of concern (VOC) after it showed a clear ability to spread much faster than other configurations of the Sars-CoV-2.

In the past 24 hours, three more analyses have been released, reinforcing some signs seen already and underscoring the next unknowns that must be determined in order to estimate the variant’s implication for the pandemic and infection control measures.

Hybrid dosing better?

A fifth antibody neutralisation study, by an Austrian team, corroborated findings by teams from South Africa, Sweden, Germany, as well as the analysis carried out by Pfizer: all show a massive drop in how antibodies bind to the Omicron variant, suggesting a hit to vaccine efficacy.

The new study adds one crucial insight: a mixed vaccine dose appeared to be more protective than two doses of the same vaccine. The antibodies from people who received a first dose of the AstraZeneca vaccine followed by a shot of the Pfizer-BioNTech vaccine showed a significantly better binding ability than antibodies elicited in those who got the same doses of Pfizer-BioNTech, Moderna or the AstraZeneca vaccine, the study found.

The Austrian study also confirmed that people with hybrid immunity – a past infection as well as a vaccine dose – were significantly protected.

Decoding transmissibility

The second new analysis was published by the UK Health Security Agency as part of its latest risk assessment and technical analysis of Sars-CoV-2 variants. The apex UK health agency now has high confidence that Omicron has a big growth advantage over Delta based on analysis of UK data “showing increased secondary attack rates” and “increased growth rates”.

The growth advantage may be due to higher resistance or an inherently better ability of the variant to transmit more readily, the assessment said, adding that “it is most plausible that it is a combination of both”.

Crucially, UKHSA refrains from drawing any inference on whether Omicron is more or less severe, citing a lack of data in these early stages of the variant’s emergence, and how the variant could impact the ability of current vaccines to prevent severe disease.

The third analysis, by Kyoto University researchers, has estimated that the variant is 4.2 times more transmissible in its early stage than Delta.

“The Omicron variant transmits more, and escapes immunity built naturally and through vaccines more,” Hiroshi Nishiura, a professor of health and environmental sciences, said in his findings, which were presented at a meeting of the Japanese health ministry’s advisory panel on Wednesday, Bloomberg reported.

Key question now

Why is the Omicron variant more transmissible? Is it an inherent trait (like it was with Alpha) or because it is leading to more reinfections? Or both?

In an interview to The Wire on Wednesday, Dr Richard Lessels, a South African infectious diseases specialist involved in the studying the Omicron that was first found in the country, said studies have shown Omicron could lead to three times more reinfections compared to other variants if it draws its superior transmissibility from a combination of both factors.

But if either factor plays a larger role, it could potentially help determine which infection control mechanism could help. A variant that is more transmissible largely because it is more resistant could likely be significantly blunted by booster doses and variant-specific vaccines (which will take time).

Since people in older age-groups are still more likely to develop severe disease irrespective of the variant, booster strategies will need to target them first.

On the contrary, if inherent transmissibility is a bigger factor, the variant could pose a larger risk to unvaccinated people since the chances of them being infected rises, and infection control could be better achieved via non-pharmacological interventions such as restrictions on gathering.

The choice, then, could come down to whether efforts need to be redoubled to reach unvaccinated people (those hesitant, or children) or to roll out boosters. Data and findings on disease severity in different ages will also inform this choice.

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