Sarc covid2

   Covid 2

     Out of the seven coronaviruses known to infect humans, the ones that have emerged since the last two decades, including SARS (fatality rate of 10 percent), MERS (fatality rate between 35-36 percent) and now SARS-CoV-2, are the ones that are a cause for worry since they are capable of causing severe illness and even death.

  Out of these three, while humans are still dealing with SARS-CoV-2 and are likely to continue doing so in the coming few years, SARS (emerged in China) and MERS (emerged in Saudi Arabia) were locally contained. The last case of SARS was detected in 2003, however, MERS is still circulating. Even so, while attempts have been made to develop a vaccine for these two coronaviruses, none of them have been approved by the US Food and Drug Administration (FDA) as of now.

     In the case of SARS-CoV-2, it was not easily contained and spread rapidly around the world. One reason for this is the spike protein of the virus, which makes it easier for the virus to enter human cells and infect the individual.

Are new Covid-19 variants detected in the US more contagious?

   While other coronaviruses also have a spike protein, this protein is slightly different in the COVID-19 causing virus compared to its close relatives. One analysis published in Nature nearly a year ago suggested that the spike protein in SARS-CoV-2 has a site on it that is activated by an enzyme in host-cells called furin. Furin is found in lots of human tissues including the lungs, liver and small intestines.

   This leaves four other coronaviruses known to infect humans which include 229E, OC43, NL63 and HKU1. The first of these was identified in the mid-1960s. But since these four human coronaviruses were mostly associated with the common cold, a need for developing vaccines for them was not felt. These four have now become endemic, which means that they keep circulating in the human population, some of them, seasonally.

What does it take to eradicate a disease?

   According to a paper published in 2016 in the Annual Review of Virology, because coronaviruses, in general, are capable of adapting to new environments through mutation and recombination with relative ease, health threats from them are constant and long term. Therefore, it is important to control their spread. Significantly, since coronaviruses are RNA viruses, they have much higher rates of mutations when compared with DNA viruses.

  Only two diseases in the world are known to have been eradicated–smallpox and rinderpest. Smallpox existed for nearly 3000 years, causing millions of deaths before it was eradicated by the use of a vaccine. The vaccine was created by Edward Jenner in 1796 and was the first successful vaccine to be developed. The last known case of the disease was detected in Somalia in 1977. But an editorial published in Lancet notes that the last cases of smallpox were recorded in Birmingham, UK in 1978.

   Rinderpest, a viral disease of cattle, on the other hand, was eradicated in 2011, with its last known case occurring in Kenya in 2001.

   But there are more than one definition of eradication.According to the American Society for Microbiology, some believe that eradication of a disease means the extinction of the pathogen, by which definition rinderpest and smallpox are not eradicated since samples of both viruses still exist in the world. In June 2019, The Pirbright Institute in the UK announced that it destroyed its final archived stock of rinderpest.

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What is the future of SARS-CoV-2?

Other definitions of eradication could mean the elimination of the occurrence of a disease in the absence of preventive measures, controlling an infection to the point at which transmission ceases within a specific area or the reduction in the worldwide incidence of infection to zero as a result of deliberate efforts.

Some of the factors that influence the eradication of a disease are: if the disease is easily diagnosable, if the disease is geographically restricted, the existence of a vaccine for the disease and if there are other hosts for a pathogen.

So, what is the future of SARS-CoV-2?

Even with the vaccine rollout across the world, it will likely take a few more years for the entire population of the world to either attain natural immunity through the disease itself or to be immune by means of a vaccine. Till then, the virus will keep circulating as it will find new hosts that are vulnerable. This means that it is likely that the disease will become endemic in the years to come.

In the study published in Science magazine, authors note that while at the beginning of an outbreak, the age distribution of cases mirrors the age of the population, once the demographics of infections reach a steady-state, the model predicts that cases will occur almost entirely in babies and young children, who have a low case fatality ratio and infection fatality ratio.

This means that once SARS-CoV-2 becomes endemic, reinfections among older individuals will happen and contribute to transmission, but because these older individuals would have already built immunity through infection acquired during childhood, they are likely to not develop severe disease and die.

But for the disease to reach this stage, it could take anywhere from a few years to a few decades. Significantly, authors note that their model recognises that in contrast with infections that are severe in childhood, in the long run, SARS-CoV-2 could join the ranks of infections that are mild and cold-causing like some other endemic human coronaviruses

Since the “severity of emergent HCoVs once they reach endemicity depends only on the severity of infection in children”, it could mean that getting infected during childhood will give enough immunity to individuals from reinfection during adulthood.