By Freeha Anjum
During this pandemic, we’ve been hearing a lot of talk about viruses and vaccines lately, but the surplus of news means may confuse you if you’re not entirely sure how these things work! Many people around the world are unaware of this, but not for long – we’re here to teach you about these invaders and how we get them out of our bodies.
First Things First: What are viruses, and How do they work?
A virus is a microscopic infectious agent which attacks living organisms in order to use the machinery of the cells in the organism to replicate itself (the cell that they use to multiply is the host cell). All viruses are composed of protein shells, called caspids, that contain DNA or RNA. Different viruses will have different genomes, and will be shaped differently – some may also have an outer envelope or glycoproteins protruding from their surface. This envelope helps the viruses enter the host cell by allowing them to fuse with the membrane of the cell. Coronaviruses contain RNA and have an outer envelope with proteins protruding off it’s surface, as you’ve likely seen in many images of the virus.
When a virus enters your body, it looks for cells to help it replicate. A virus then injects it’s genes into the cell, or in some cases the entire virus absorbs itself into the cell. Within the cells of living organisms, there are many proteins and enzymes that allow us to copy our genes so that we can produce more cells. Viruses use our cell machinery to replicate their genes instead. Doing this means that many new viruses will be formed inside the cell, and when they leave they may rupture the membrane, thus killing the cell. Some viruses may not rupture the cell, or may wait longer before producing more copies of itself, but ultimately the goal for all viruses is the same: to make more of itself using our cells.
So, How does our body fight off viruses?
Let’s talk a bit about the human immune system. When a virus invades the human body, there are three mechanisms we can use to fight it.
- Cytotoxic T Cell
Cells use molecules, called class I major histocompatibility complex proteins (MHC class I), to show pieces of proteins from inside the cells on their surface. This means that if a cell has a virus in it, this will be apparent by the viral proteins on the cell’s surface. Cells known as cytotoxic helper T cells can detect these viral protrusions through receptors, and can kill the cell by releasing cytotoxic factors.
Some viruses have learned to adapt to these T cells, however, and stop them from using the MHC class I proteins to protrude the virus material on the cell’s surface. Luckily, our bodies have a defense mechanism for this circumstance, too: natural killer cells are able to detect cells that have fewer MHC molecules, and release materials which kill the cell.
Another way for cells to fight back against viruses is through interferons, which are proteins created by infected cells. Interferons produce signals for other cells to be warned about the presence of a virus. This allows for the surrounding cells to increase the MHC class I molecules on their surface, so that cytotoxic T cells can quickly identify infected cells and eliminate them.
A third way for the body to destroy viruses, which you have likely heard of before, is through antibodies. These are proteins that can recognize viruses and bind to them so that they cannot inject their genetic material into other cells. If antibodies work together, they can make the viruses stick together in a process known as agglutination, which makes them easier to destroy. Antibodies can also activate cells called phagocytes, which engulf and kill the host cell in a process known as phagocytosis.
What do vaccines do?
There are many different types of vaccines, used on different viruses and for different practical applications – let’s talk about three common types.
- Attenuated Vaccines (Live)
These vaccines involve taking a version of the virus that is weak, so that it does not cause any serious diseases in people. By inserting this virus into the body, the immune system can learn to fight it off, likely by building antibodies. This vaccine cannot be used on individuals with weak immune systems, however, as those individuals may not have the ability to fight off the weakened virus.
- Inactivated Vaccines
Inactivated vaccines are made by taking a dead virus and inserting it into the body. Even though the virus is dead, the body can still learn from it and help it’s immune system to help fight it, although it is not as effective as a live vaccine, so oftentimes multiple doses are necessary to build up the immune system.
- Subunit Vaccines
These vaccines include parts of a virus, instead of the entire agent. This works similarly to the other vaccines above, but includes less side effects due to only containing essential antigens.
For more information specific to coronavirus vaccines, read the article written by Aiman Altaf here.
What is Herd Immunity?
After all this virus talk, you’ve probably heard of the term herd immunity. But what does this mean, and how does it relate to virus elimination?
The idea of herd immunity is that enough of the population will be immune to the virus in question – i.e. vaccinated – to protect the smaller part of the population which cannot be vaccinated for health and other reasons. Many people misunderstand herd immunity, believing that it means the entire population should be exposed to the virus, so that people can get sick and build antibodies. This is hardly the case – herd immunity is done after a vaccine for a particular virus is created. The vaccine is then distributed to as much of the population as possible, in hopes that those who are not vaccinated will still be safe from the virus.
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