Why is Omicron More Infectious Than Delta? New Data Shed Some Light

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Data finds the Omicron COVID-19 variant spreads 4 times faster than any previous variant, including the highly transmissible Delta.

Shedding light on why this might be, multiple recent studies indicate that the reason could be that this particular variant multiplies in the airways of the infected person faster than in the lungs, making it highly transmissible.

According to preliminary findings of one ex vitro lab study conducted in Hong Kong, the Omicron variant multiplies in the human bronchus 70 times faster than Delta and the original strain of SARS-CoV-2.

Another preprint study conducted in collaboration between scientists from Harvard and MIT universities in the US, corroborated these findings, and said Omicron spreads 4 times faster than the original strain, and even faster than Delta.

The findings of these studies—Although some are yet to be peer reviewed—are important as they may help scientists crack the code to Omicron's behaviour in the future and how to tackle it.


Let's break down what these studies have found so far.

New Revelations about Omicron 

  • Higher viral load in the airways than lungs.

The first study, from Hong Kong, not only found that within the first 24 hours of infection, Omicron multiplies 70 times faster than Delta in the respiratory tract, but at the same time, infection in the lungs was found to be 10 times lower as compared to Delta and the original strain.

This last part could actually mean good news, but assuming the variant will cause less severe illness based solely on this may be dangerous.

"‘It is important to note that the severity of disease in humans is not determined only by virus replication but also by the host immune response to the infection, which may lead to dysregulation of the innate immune system, i.e. “cytokine storm," said Dr Michael Chan Chi-wai, Principal Investigator, Centre for Immunology and Infection (C2i), Hong Kong Science and Technology Park (HKSTP) in a press release.

Its also important to note that this particular study was ex vitro, which means it was conducted on human tissue in the lab. So, the next step would be for clinical trials to confirm these findings.

Omicron multiplying in the airways vs the lungs.

(Photo: HKU medicine)

The study authors concluded that given Omicron's ability to circumvent vaccine protection and its highly infectious nature, it is likely to cause significant damage even it is less pathogenic.

  • Omicron can escape vaccine immunity, but boosters can help.

The other study, conducted in the US measured neutralization potency of sera from 88 people who had received Moderna vaccine, 111 people who received Pfizer, and 40 people who got the Johnson & Johnson vaccine against wild type, Delta, and Omicron SARS-CoV-2 pseudoviruses.


The participants also included people that were vaccinated recently (within 3 months of the study), distantly (6-12 months), or recently boosted, and accounted for prior SARS-CoV-2 infection.

The findings of this study confirmed previous studies that pointed to vaccine efficacy waning over time for all variants.

"While Delta neutralization became undetectable in most individuals vaccinated >6 months before blood draw, Delta neutralization was detectable and only modestly decreased in recently vaccinated, previously infected, and recently boosted vaccines," it read.

Interestingly, neutralization of Omicron was undetectable in most vaccinated individuals.

According to the study, this happens because in the case of Omicron, the mutations are structurally focused at the top of the spike, in regions accessible to antibodies.

However, people who received a third booster shot with mRNA vaccines exhibited potent neutralization of Omicron only 4-6-fold lower than wild type, "suggesting that boosters enhance the cross-reactivity of neutralizing antibody responses," said the study authors.

This study also confirmed that the Omicron pseudovirus is more infectious than any other variant tested.

According to the findings of this study, the Omicron COVID variant is up to 4 times more infectious than the original strain.

What this means for the future of the COVID pandemic

Some experts have talked about how increased transmissibility could mean that the virus is turning more infectious but less virulent.

According to one study published on Tuesday, 14 December, that collated data from 77 previous studies, about 40 percent of COVID-19 cases now globally are asymptomatic.

However, if a large number of people having mild to no symptoms, it could lead to the virus spreading even faster as cases may go undetected and people slack in following COVID-19 protocol.

More cases inevitably mean a higher number of hospitalisations, and this could burden the healthcare system in the coming months.

The Omicron COVID-19 variant was first identified on 19 November in a lab in Botswana Harvard HIV Reference Laboratory, and on 26 November it was declared a variant of concern by the WHO.

Since then, scientists have been scrambling to decode this new variant with COVID graphs around the world seeing an upward trend.

It may be too early to sound the alarm bells, but given what we know about the virus so far, experts advise erring on the side of caution and remembering that the pandemic is not over yet. So, mask up, maintain social distancing and get vaccinated if you already haven't.

(At The Quint, we are answerable only to our audience. Play an active role in shaping our journalism by becoming a member. Because the truth is worth it.)

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Topics:  COVID-19   COVID Variant   Delta Variant 

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