Omicron may be less likely to cause severe disease

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In a new study from the University of Cambridge, researchers found Omicron may be much better at evading vaccine-induced immunity, but less likely to cause severe disease.

They created synthetic viruses—known as ‘pseudoviruses’—that carried key mutations found in the Delta and Omicron strains. They used these to study the virus’s behavior.

The team tested the pseudoviruses against blood samples donated to the NIHR COVID-19 BioResource.

The blood samples were from vaccinated individuals who had received two doses of either the AstraZeneca (ChAdOx-1) or Pfizer (BNT162b2) vaccines.

On average, Omicron required around a ten-fold increase in the concentration of serum antibody in order to neutralize the virus, compared to Delta.

Of particular concern, antibodies from the majority of individuals who had received two doses of the AstraZeneca vaccine were unable to neutralize the virus. The data were confirmed in live virus experiments.

Reassuringly, however, following a third dose of the Pfizer vaccine, both groups saw a big increase in neutralization.

The team says the Omicron variant appears to be much better than Delta at evading neutralizing antibodies in individuals who have received just two doses of the vaccine.

A third dose ‘booster’ with the Pfizer vaccine was able to overturn this in the short term, though they will still expect a waning in immunity to occur over time.

Spike proteins on the surface of SARS-CoV-2 bind to ACE2, a protein receptor found on the surface of cells in the lung.

The team says that the more efficient the virus is at infecting cells, the more severe the disease might be.

The fact that Omicron is not so good at entering lung cells and that it causes fewer fused cells with lower infection levels in the lab suggests this new variant may cause less severe lung-associated disease.

Overall, the study suggests that Omicron’s mutations present the virus with a double-edged sword: It’s got better at evading the immune system, but it might have lost some of its ability to cause severe disease.

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One researcher of the study is Professor Ravi Gupta.

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