Less protection from past infection, likely reduced vaccine efficacy: IHME on Omicron

For now, best to assume Omicron causes as severe a disease as Delta, IHME says

By Taran Deol
Published: Wednesday 08 December 2021
The Omicron Variant. Photo:

An independent population health research centre in the United States has stated that the new Omicron variant of the novel coronavirus (SARS-CoV-2) has more potential to escape immune response and the effect of vaccines.

The comments by the director of the Institute for Health Metrics and Evaluation (IHME), at the University of Washington Medicine, US, are worrying as the characteristics of Omicron are still unclear.

Christopher JL Murray, the director of IHME, cited yet-to-be-released data from South Africa in his weekly insight. He said:

From a theoretical basis and a number of lab studies, as well as some neutralising antibody-type studies, there’s reason to believe that there will be less protection from past infection (so more immune escape) and likely reduced vaccine efficacy.

However, he also underlined how “the reduction of vaccine efficacy for preventing infection may be quite a bit larger than the reduction of vaccine efficacy in preventing severe disease and death.”

Murray also noted as to how quickly the Delta variant was replaced by the Omicron variant in South Africa. This trend could likely be replicated in other parts of the world as well.

It is unclear as to whether Omicron may cause more severe cases as both mild and severe cases are being reported from South Africa. However, there has been an increase in hospitalisation.

“In the past when we’ve seen new variants emerge, like Alpha, it took more time for rapid transmission from younger groups to spread into older groups at greater risk of hospitalisation,” Murray noted.

He added that at present, it was best to assume that Omicron caused as severe a disease as Delta. It was a factor that might change depending on new information in the coming few weeks.


Omicron’s ability to evade immunity acquired through natural infection is a concerning factor for many, particularly those countries where older variants caused widespread disease.

In India, for instance, the Delta variant remains prevalent, while the Gamma variant is rampant in Latin America.

“We would expect some cross-variant protection, but given all the mutations in the spike protein, it’s likely greatly reduced. But it’ll take quite some time until we’ll be sure,” Murray said.

While there have been reports of low protection from past infections, a reinfection factor the WHO had warned of November 28, more data is needed to be certain.

Vaccine immunity against infection wanes over time. Several studies, yet to be peer-reviewed, underline a five-month time period following which the number of antibodies start decreasing.

It is as yet unclear whether Omicron can fully evade vaccine immunity. But Murray argued that “there’s more resilience of the immunity from vaccination for hospitalisation and death, but we expect some reduction due to the mutations in the spike protein.”

He also underlined three key factors that would help mitigate a possible rise in cases as Omicron spread to over 40 countries.

These include continuous high-quality masking, boosting immunity through widespread vaccination drives and reducing the spread of the virus from incoming travellers by screening them thoroughly. 

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