Covid-19: Asymptomatic or falling ill in case of infection?

 

One of the biggest mysteries of Covid-19 has been why some people become very ill, while a large number of people who are infected show no symptoms at all. It turns out that this protection may be linked to the most mundane of illnesses…the common cold.

 It may turn out that a common cold which you may have acquired some time back may actually be helping you fight off Covid-19. How is this possible? The answer to this has to do with the shape and structure of viruses.

 A virus is a microscopic (very tiny) particle that multiplies itself in a host organism. Viruses can infect all life forms, from plants to animals to humans and even bacteria! Once they enter inside the host, they hijack the host cells' machinery to perform a single task: make more copies of themselves. Viruses thus disrupt the normal activities of cells and replicate themselves. Viruses contain a nucleic acid (DNA or RNA) that is surrounded by a coat of proteins. The nucleic acid is the genetic material and contains the blueprint (or instructions) for making additional copies. The proteins of the virus act on the instructions provided by the nucleic acid. Put simply, the nucleic acid is like a general who gives instructions and the proteins are like soldiers who execute those instructions.

 While the virus responsible for this current pandemic is commonly called “the coronavirus” it is not the first or only coronavirus. There are many different types of coronaviruses. A coronavirus just refers to a virus that has protein spikes on its surface, as this makes it look a bit like a crown (corona) when viewed under a microscope. The viruses that caused the SARS (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome) outbreaks were also coronaviruses. And so are some of the viruses that cause the common cold.

 The outside surface of a coronavirus is made up of several different protein molecules, which together form a sphere to encapsulate the RNA molecule that holds all of the instructions for making more virus. There are S, M, and E proteins on the surface of the coronavirus. 

Each coronavirus has a slightly different set of instructions written in its RNA, and thus makes slightly different S, M, and E proteins to be displayed on the surface. But, while each combination is unique, some viruses are related and have similar versions of specific proteins.This is similar to lego blocks. You can use the lego blocks in different combinations to make many different variations of the same house that you are building. 

 So, what does this all have to do with asymptomatic Covid-19 infections? That comes down to how your body recognizes and deals with viruses. When you’re infected, your immune system makes molecules called antibodies. These antibodies attack the proteins on the surface of the virus. And, your immune system doesn’t always stop with just one virus protein. You can make antibodies for different proteins, or even different parts of a protein (these are called “epitopes”).

 Your body uses these antibodies to fight the infection and then remembers how to make them in case you see that virus again in the future. In fact, that’s how vaccines work – they teach your body to make antibodies, but without you having to be infected.

 The interesting discovery that scientists have made is that human blood samples from before Covid-19 actually contain antibodies that are able to bind to the SARS-CoV-2 virus that causes Covid-19. This means that people who were previously having common cold, SARS or MERS from a coronavirus strain successfully generated antibodies that are also able to bind to the proteins on the Covid-19 virus.

 The hypothesis is that when these individuals encounter Covid-19, they are able to produce these antibodies and fight off the infection without showing symptoms. In fact, the high exposure of children to cold viruses may explain their high rate of asymptomatic Covid-19 infection.

 Scientists are just starting to test this hypothesis, but if it does turn out to be correct, that would mean that nature has already given some of us a Covid-19 vaccine…in the form of that seemingly pesky cold that we had some time back.  Either way, this remains a hypothesis, but one that could explain immunity to Covid-19.

 However, there is an important point to be noted. Not all common colds are produced by coronaviruses. There are some colds that are due to infection by rhinovirus, a different type of virus. People who have been infected by rhinovirus may not be able to fight off Covid-19 since their antibodies are not specific to coronavirus. These people may be the ones that may develop symptoms to Covid-19.

Finally, what does all of this mean? It means that irrespective of anything, you must wear a mask and follow safe practices till a vaccine is actually rolled out.