Omicron v Delta: How do variants compare on infectiousness and effect on Covid vaccines?

A woman receives her Covid-19 booster jab (Yui Mok/PA) (PA Wire)

The emergence of the new coronavirus variant Omicron has already affected travel rules and seen a return to mandatory masks on public transport in England.

Some 336 confirmed cases of the variant have been detected in the UK as of Monday, as scientists race to fully understand the new strain.

One expert warned that Omicron could become our dominant strain within just weeks.

A full picture of the threat the variant poses is still to emerge. But what do we know about Omicron and how does it compare to Delta?

When they were discovered

Delta: It was first discovered in India last December before rapidly spreading to the UK. The variant is still the main dominant strain, as it is in many countries.

Last week the ONS said that 99 per cent of sequenced cases in the UK were Delta ending the week November 27.

Omicron: UK scientists became aware of Omicron on November 23, after samples were uploaded to a coronavirus variant tracking website from South Africa, Hong Kong and then Botswana.

However, it is likely that the variant was in circulation earlier than that date but was not sequenced.


Delta: Delta has 13 mutations, of which nine are in the ‘spike protein’. According to the ONS, scientists can differentiate Delta from Omicron by identifying patterns among three genes in positive results – the S gene, the ORF1ab gene and the N gene.

Delta infections usually test positive for all three genes, whereas the Omicron variant tests negative for the S gene.

Omicron: Omicron has the most mutations of any variant of SARS-CoV-2, the virus that causes COVID-19. It caused alarm among scientists because at least 32 of its mutations are in the spike protein.

The spike protein is part of the virus which helps it latch onto our cells, fitting cellular receptors “like a lock and key,” say Yale University researchers.

While Omicron has more mutations in total, Robert Garry, a virologist at Tulane University, told CNN that the number of mutations don’t automatically translate to a more dangerous virus.

How contagious are they?

Delta: The Delta variant was more than 2x as contagious as variants that came before it, according to the Centre for Disease Control in the United States.

The incubation period was also shorter than previous iterations of SARS-CoV-2, with a mean time of 4 days, meaning people became infectious sooner.

(AFP via Getty Images)

Omicron: It is still unclear whether Omicron is more transmissible compared with other variants, including Delta, according to the World Health Organisation.

However, a rapid rise of people testing positive for Covid in areas of South Africa affected by the variant has sparked studies to determine whether this is because Omicron is more easily passed on.

How severe is illness?

Delta: According to a study published earlier this year, those who got the Delta variant were twice as likely to be hospitalised as a result of their illness than if they had the earlier Alpha variant.

However, the vast majority of those in the study, 70 per cent, were unvaccinated as the cases occurred very early on into the vaccine rollout.

Omicron: A full picture is yet to emerge on whether Omicron is likely to cause more deaths or severe disease than Delta, and understanding this is likely to take several more weeks, the WHO has said.

However, scientists have warned that very high levels of even a mild illness could be challenging for the NHS if it results in enough hospitalisations For this reason, Dr Simon Clarke, a microbiologist at the University of Reading, told the Mail Online that it was “entirely possible” that Omicron could trigger a wave of hospital admissions on par with the peak in January 2021.

(PA) (PA Wire)

Vaccine escape

Delta: Two doses of either Oxford or Pfizer jabs provides at least the same level of protection as having had Covid-19 before, according to a study earlier this year. Two doses of the Pfizer/BioNTech or Oxford/AstraZeneca vaccine were estimated to be 95 per cent and 92 per cent effective against hospitalisation with the Delta variant, respectively, according to the ONS.

Omicron: Deputy chief medical officer for England Professor Jonathan Van-Tam has said that Omicron’s mutations “makes us worry about a possible effect on vaccine effectiveness”.

But booster vaccines may well offer good protection in the face of the variant, experts behind a major new study have suggested.

A team studying the effects of third doses said the body’s T cell immune response after a booster shot is such that it may provide protection from hospital admission and death.

Pfizer expects its Covid-19 vaccine to hold up against the variant and data on how well it protects should be available in the coming weeks according to senior executives at the company.

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