Omicron is quickly overtaking the Delta variant of Covid-19 and becoming dominant around the world, a senior WHO official has warned, with the global health agency cautioning that there is "increasing evidence" Omicron is able to evade immunity but has less disease severity as compared to other variants.
It could take some time for Omicron to overtake Delta in some countries, because it depends on the level of circulation of the Delta variant in those countries, Infectious Disease Epidemiologist and Covid-19 Technical Lead at the World Health Organisation (WHO) Maria Van Kerkhove said on Tuesday.
"Omicron has been detected in all countries where we have good sequencing and it's likely to be in all countries around the world. It is quickly, in terms of its circulation, overtaking Delta. And so Omicron is becoming the dominant variant that is being detected," Kerkhove said during a virtual questions and answers session.
She further cautioned that even though there is some information that Omicron causes less severe disease than Delta, "it's not a mild disease" because "people are still being hospitalized for Omicron."
The COVID-19 Weekly Epidemiological Update, released by the WHO, said that over 15 million new COVID-19 cases were reported globally in the week of January 3-9, a 55 per cent increase as compared to the previous week when about 9.5 million cases were reported.
Over 43,000 new deaths were reported in the past week. As of 9 January, over 304 million confirmed COVID-19 cases and over 5.4 million deaths have been reported.
The highest numbers of new cases were reported from the US (4,610,359 new cases; a 73 per cent increase), France (1,597,203 new cases; a 46 per cent increase), the UK (1,217,258 new cases; a 10 per cent increase), Italy (1,014,358 new cases; a 57 per cent increase) and India (638,872 new cases; a 524 per cent increase), the update said.
Kerkhove said the 15 million cases reported in the last seven days are a "record high in this pandemic" and are an "underestimate" given the challenges in surveillance around the world and COVID-19 self-tests at home that are not registered.
The WHO update said that the Omicron variant has a substantial growth advantage and is rapidly replacing other variants.
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"This variant has been shown to have a shorter doubling time as compared to previous variants, with transmission occurring even amongst those vaccinated or with a history of prior SARS-CoV-2 infection; there is increasing evidence that this variant is able to evade immunity," the update said.
It said that in terms of disease severity, there is growing evidence that the Omicron variant is less severe as compared to other variants.
Citing a non-peer-reviewed retrospective cohort study from the US, the update said the findings suggest that while the absolute number of cases and hospitalisations among children are currently increasing in the US, the risk of hospitalisation still remains lower compared to other age groups during the period when Omicron is circulating as compared to the period when the Delta variant was dominant.
The update also noted that since December, six studies have provided evidence of reduced vaccine effectiveness (VE) of COVID-19 vaccines against the Omicron variant.
"While early VE estimates against the Omicron variant should be interpreted with caution due to potential biases, these preliminary results provide evidence of reduced overall effectiveness of vaccines against the Omicron variant, with greater declines in effectiveness with increasing time since vaccination, relative to Delta... While a booster vaccination appears to improve VE against infection and hospitalisation due to the Omicron variant, more data are needed to assess both the magnitude and duration of the protection," the update said.
The WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) said that as coronavirus evolves, the composition of current COVID-19 vaccines may need to be updated, to ensure that "COVID-19 vaccines continue to provide WHO-recommended levels of protection against infection and disease by VOCs, including Omicron and future variants."
Kerkhove added that as Omicron enters and circulates among vulnerable populations, "we will see increase in hospitalisations and deaths. So please treat this virus as seriously as it needs to be treated. The narrative that it's the common cold is not true. The narrative that it is just mild is not true. So we have to really fight against it. It's not the time to give up."