Evidences so far suggest that Omicron variant of SARS-CoV-2 has high transmission rate but fortunately is low on virulence and is not usually leading to severe symptoms of COVID-19 disease or deaths. But existing vaccines seem to be less effective as number of breakthrough infections have been reported. In the event of large number of Omicron cases with symptoms requiring in-patient hospital care, there is a possibility of health system being overwhelmed. However, much more serious threat posed by the Omicron variant is the possibility of emergence of any new variant with higher virulence as a result of innumerable serial passages (transmissions) of the viruses among the people. Apparently, this is how the highly virulent delta variant had come into being from the earlier variants through very high degree of transmission among the people. Therefore, restricting passage of the virus among people i.e., breaking transmission chain through the use of facemasks, physical distancing and discouraging gatherings is the key.
There is report of Omicron and cold-like symptoms rapidly taking over in London.
According to ZOE COVID Study, in total there are currently 87,131 new daily symptomatic cases of COVID in the UK on average. An increase of 4% from 83,658 new daily cases last week. Running nose, headache, fatigue (either mild or severe), sneezing and sore throat were the top five symptoms reported. Cold-like symptoms appear to be the predominant feature of Omicron. In the fully vaccinated population, there are currently 27,000 new daily symptomatic cases in the UK. An increase of 6% from 25,411 new daily cases last week1.
In view of extensive mutations, it was expected that Omicron variant would evade immune responses to some extent. In a study on individuals who had received routine two doses plus a booster dose of mRNA vaccines, all patients were found to experience mild to moderate COVID-19 symptoms giving impression that even three doses of mRNA vaccines may not be sufficient to prevent infection and symptomatic disease2. Similarly, in another study involving administration of booster doses of inactivated virus COVID-19 vaccine BBIBP-CorV, the researchers observed a significant rebound in neutralizing immune response against SARS-CoV-2 however the Omicron variant showed extensive but incomplete escape of the booster elicited neutralization3.
Notwithstanding vaccine breakthrough cases, Omicron cases are usually not associated with severe COVID-19 symptoms. Only one Omicron related death has been reported in the UK till date. However, in the event of large number of Omicron cases with symptoms requiring in-patient hospital care, there is a risk of health system being overwhelmed. But much serious threat is associated with its highly infectious nature.
It is established that Omicron variant is over four times more infectious or transmissible than the delta variant. In less than a month since Omicron was reported first in South Africa, it has spread worldwide. Initially, the detected cases were travel-related, but now most of the affected countries are witnessing high level of community transmission. High transmission rate is a matter of concern because numerous serial passages of the virus among the infected people may contribute in emergence of more virulent variant in future.
Coronaviruses lack proofreading nuclease activity of their polymerases hence replication errors remain uncorrected which accumulate and contribute in mutations. More transmissions mean more replication errors hence more mutations accumulate in the viral genome leading to emergence of new variants. Human coronaviruses have been building up mutations to create new variants in the recent history4. Apparently, this is how the highly virulent delta variant had emerged from the earlier variants through very high degree of transmission among the people.
With Christmas and New Year celebrations on its way, the risk of emergence of any new variant with higher virulence as a result of innumerable serial passages (transmissions) of the viruses among the people has forced many countries such as Netherland, UK and France to impose lockdown like restrictions.
Limiting transmission and breaking the transmission chain is the key. The good old practices of use of facemasks, physical distancing and avoiding large gatherings should be very helpful.
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References:
- ZOE COVID Study, 2021. Data Press Release – Omicron and cold-like symptoms rapidly taking over in London. Published December 16, 2021. Available online at https://covid.joinzoe.com/post/omicron-and-cold-like-symptoms-rapidly-taking-over-in-london
- Kuhlmann C., et al 2021. Breakthrough Infections with SARS-CoV-2 Omicron Variant Despite Booster Dose of mRNA Vaccine. Published: 9 December 2021. DOI: http://dx.doi.org/10.2139/ssrn.3981711
- Yu X., et al 2021. Pseudotyped SARS-CoV-2 Omicron variant exhibits significant escape from neutralization induced by a third booster dose of vaccination. Preprint medRxiv. Posted December 18, 2021. DOI: https://doi.org/10.1101/2021.12.17.21267961
- Prasad U., 2021. Variants of Coronavirus: What We Know So Far. Scientific European. Posted 12 July 2021. Available online at http://scientificeuropean.co.uk/covid-19/variants-of-coronavirus-what-we-know-so-far/
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