The newly-emerged Omicron variant has been ringing alarm bells in the world. But could it be the first step towards Covid-19 becoming an endemic? And if yes, how would that be good for the world? According to reports, the virus is now spreading ‘faster than ever’ in South Africa, where the variant first emerged, but there are early indications that omicron may cause less severe illness than other forms of the virus.
Researchers at a major hospital complex in Pretoria told the New York Times that their coronavirus patients are much less sick than those they previously treated, and that other hospitals are seeing similar trends. In fact, they claim that the majority of their infected patients were admitted for other reasons and do not exhibit Covid-19 symptoms.
Compared to this, the deadly Delta variant was proved to cause increasing severity of the disease in patients, resulting in more deaths. While early data suggests that the Omicron variant is even more transmissible than Delta, with an increased possibility of breakthrough infections (cases in those vaccinated), a milder illness through the variant may help the raging pandemic become an endemic, some experts opine.
What’s an Endemic Stage?
But first, let’s know what an endemic stage actually signifies. The endemic stage of any disease is reached when a large portion of the population develops immunity to the disease, either through vaccination or antibodies acquired from a previous infection. The disease’s spread begins to slow at this point, according to epidemiologist Dr. Lalit Kant. in a BBC report.
Dr. Shahid Jameel, a prominent virologist, told the BBC that an endemic does not preclude infection. “It simply means that it does not spread disease.”
Endemic diseases include chicken pox and malaria, which have a predictable number of cases each year in certain parts of the world.
According to a 1948 definition cited in the Indian Journal of Endocrinology and Metabolism, “an endemic area is one in which there is a practically continuous presence of clinical cholera with annual seasonal exacerbation of incidence,” a report in the Indian Express states.
When Does an Epidemic Become an Endemic?
According to one mathematical model published in the Journal of Epidemiology and Community Health, if R0, the rate at which the virus is transmitted, equals 1, the disease is endemic. When R0>1, it indicates that the disease is spreading and will eventually become an epidemic. If R0<1, it means that the number of cases of the disease is decreasing.
R0 denotes the number of people infected by a disease-carrying individual.
What About Covid?
While the exact timing is difficult to predict, most scientists agree that the Covid-19 pandemic will end and the virus will become endemic, a report in the Guardian States. That means the virus will almost certainly never be completely eradicated, but as more people are immunised and exposed to it, infections will eventually occur at a consistently low rate, and fewer people will become severely ill. A region with high vaccination and booster rates will most likely experience endemicity sooner than a region with lower rates.
Omicron First Step Towards Endemicity?
A leading infectious diseases specialist who monitors variants for a Harvard Medical School-led research collaboration told the Associated Press the world is witnessing “what appears to be an exponential increase of Omicron over Delta.” “It’s still early days, but data is starting to trickle in, indicating that Omicron is likely to outcompete Delta in many, if not all, places,” Dr Jacob Lemieux said.
“There’s still a lot of uncertainty … but when you put the early data together, you start to see a consistent picture emerge: that Omicron is already here, and based on what we’ve observed in South Africa, it’s likely to become the dominant strain in the coming weeks and months and will likely cause a surge in case numbers,” Lemieux added.
These are very early days in terms of our understanding the Omicron variant. What is known is that it has a large number of mutations, particularly in the spike protein and it appears to be rapidly spreading in specific parts of the world. Very early indications from Africa suggest it does not cause particularly severe disease (though the World Health Organization has urged caution given the limited data available).
At this point, it isn’t clear whether it has any greater capacity to evade vaccines than other SARS-CoV-2 strains such as Delta. It is very common for viruses to become less virulent (that is, cause less severe disease) once they become established in a population. The classic example is myxomatosis, which killed 99% of rabbits when first introduced into Australia, but which now causes much lower mortality.
Some experts have predicted COVID will also become less severe as it transitions to an endemic level of disease settling into a predictable pattern of infections in a given location. It’s possible the Omicron variant may be the first step in this process. Why some variants become dominant Evolutionary biology suggests variants are more likely to thrive if they increase more rapidly in the human population than current strains. This means two things: strains with a higher R number (the basic reproduction number, or the average number of people an infectious person will likely infect) will replace those with a lower R number.
Additionally, strains that lead to the host being infectious earlier will replace those that take longer to become infectious. So strains with a shorter incubation period replace those with a longer incubation period. This appears to be the case with Delta, which has a shorter incubation period than the strains before it. Viral strain evolution needs to be considered in the particular population in which the variant appears. Disease evolution is expected to work differently in a population with low levels of vaccination compared to one with higher levels of vaccination.
In a largely unvaccinated population, like South Africa where roughly 25% of the population is vaccinated and the Omicron variant was first detected, strains with a high R number will stand a better chance of taking hold. But in a highly vaccinated population, strains that are better able to evade the vaccine will be more likely to dominate, even if they have a lower R number in unvaccinated people. Less severe symptoms may fuel spread So, would you expect a variant with less severe COVID symptoms to thrive? It really depends on the trade-offs between symptoms and transmissibility.
The Game of Viraemia
If symptoms are less severe, people are less likely to come forward to be tested and therefore are less likely to isolate. Some may not realise they have COVID at all. Therefore, a strain with low virulence (meaning it has a lower ability to cause severe symptoms in the body) may be better able to transmit to more people than highly virulent strains. On the other hand, as appeared to be the case for Delta, some variants can cause higher viraemia than others meaning higher levels of the virus within infected people’s bodies. The more virus present, the more likely the person is to be able to successfully transmit the disease. This is because of the dose-response relationship the higher the infective dose, the more likely it is an infection will result.
Again, all things being equal (without yet knowing the details of exactly how specific mutations behave), higher levels of viraemia are likely to lead to more severe symptoms. It is not clearly understood yet why Omicron is apparently highly transmissible at least in the African context, so at this stage we don’t know whether it produces higher levels of viraemia than other strains. Viral transmission is a complex multistage process, so many things may be responsible for Omicron’s high transmission rate.
Vaccination is Most Important
Watch and wait What happens next is yet to be determined. Experts will look for more information on the transmissibility of Omicron, the level of viraemia it generates and the extent to which it is capable of evading either the existing vaccines or immune responses resulting from previous infection. Omicron may well behave quite differently in a highly vaccinated population such as we now have in Australia compared with a population with very low levels of vaccination as is the case in most of sub-Saharan Africa. Nevertheless, the emergence of this new variant emphasises an effective vaccination effort worldwide is necessary to overcome the COVID pandemic.
With inputs from the Conversation, New York Times.
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