The world has witnessed the coronavirus epidemic by SARS-CoV in 2003, epidemic by MERS-CoV in 2012, and pandemic by SARS-CoV2 in 2020 (Covid-19)

Question

The world has witnessed the coronavirus epidemic by SARS-CoV in 2003, epidemic by

MERS-CoV in 2012, and pandemic by SARS-CoV2 in 2020 (Covid-19). Is it possible that

due to the antigenic shift of SARS-CoV virus, a new subtype of the virus (Covid 19) is

generated that cause this pandemic in 2020?

Answer 1

SARS-CoV1, MERS-CoV, and SARS-CoV2 are related to each other but not direct descendants. Essentially, they're similar but it's not like SARS-CoV1 turned into MERS-CoV which then turned into SARS-CoV2. Antigenic shift refers to the process by which as viruses adapt to their host, they accumulate mutations which make their antigens change very slowly over time. Vaccines (and our immune system) recognize these antigens in order to mount an attack to clear the infection. As the antigens slowly change, our immune systems may be less likely to recognize them. If this happens slowly, it's not usually a big deal and our immune systems adapt as the viral antigens change. Deadly flu pandemics occur when influenza antigens change rapidly -a process called antigenic SHIFT. That's beyond the scope of this question, but I wanted to provide an example of how antigens can change quickly and cause problems for us.

All coronaviruses are similar -in fact, there are mannnyyy types that cause nothing more than the sniffles or the common cold. The more famous examples, mentioned above, cause more severe disease for a variety of reasons that are, again, beyond the scope of your question. That being said coronaviruses are commonly found in the bat population (among other animals). SARS-CoV1 and SARS-CoV2 are examples of zoonotic diseases, where a pathogen initially just infects an animal but eventually gains the ability to not only infect humans, but spread human to human.

A phylogenetic analysis (link to paper: https://pmc.ncbi.nlm.nih.gov/articles/PMC10369958/) in 2023 found that SARS-CoV1 and SARS-CoV2 likely shared a most recent common "ancestor" within 1-3 years of the emergence in humans. So, these two viruses are closely related. Most likely, they were circulating together with many other coronaviruses where they underwent antigenic drift. This is one of the reasons coronaviruses in particular can cause havoc with their outbreaks, because of how easy it is for their antigens to "evolve." To the best of my knowledge, though, the data is showing that SARS-CoV1 and SARS-CoV2 are "siblings" rather than "parent-child."