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Viruses and Vaccines: How They Work

You certainly hear enough about both viruses and vaccines these days, but how much do you actually know about them?

When I asked myself this question, answer was: “surprisingly little.”

This world is wonderfully complex; it is impossible to have a working knowledge of all of it’s complexities. That’s simply too much for any brain to handle. But having a basic understanding of a diverse range of topics is, in my opion, both desireable and possible. The secret is to keep it simple and focus only on the most generalizable and basic concepts within each domain. Being able to represent the information graphically certainly does not hurt either.

So, here is what I have learned over the past few weeks (or maybe months, it’s hard to tell sometimes). I hope you find it useful and enjoyable.

What is a virus and how does it work?

First, let’s start with the anatomy of a virus. There are, of course, various viruses (each with its own specific traits), but certain elements are common for most viruses:
1. a core with DNA or RNA,
2. a body with protein spikes, and
3. various enzymes.

As with most creatures, the “goal” of the virus is to multiply and spread. To this aim, the DNA/RNA can be thought of as the blueprints of the virus, containing all the necessary information for replicating the virus. However, the virus itself does not contain the necessary production facilities to perform the replication. This is where the protein spikes come in to play.

Utilizing the protein spikes, the virus binds to, then enters the cell of a host — for instance, when you get infected with a virus, you are the host. Since your cells contain all the necessary production capacities required to replicate the virus — these are the same production capacities used in the daily operations of healthy cells — the virus hijacks the production line and uses it, in conjunction with its own DNA/RNA, to replicate itself. From there, the new copies of the virus exit the cell and go on to look for new factories to break into and use to replicate themselves further.

How does your body protect itself from a virus?

Naturally, your body does not like that this unwelcomed guest is using its resources for malicious purposes. When the virus is detected, your body launches a defensive effort to kill the virus and stop it from spreading. Part of this effort consists of making antibodies that stop the virus from entering your cells.

Antibodies work by binding to the protein spikes, thus neutralizing the virus’s ability to bind to and enter cells. In fact, antibodies cannot enter cells either and can only neutralize viruses that are intercellular (between cells).

As you can see in the depiction on the right, the antibody fits perfectly to the protein spike in the virus. Since most viruses have differently shaped protein spikes, your body needs to develop new antibodies when it encounters novel viruses. Once a particular virus has been encountered, however, your body will keep the information about how to create the antibodies to protect itself from that virus in the future. This ability is often called immunological memory and is how you gain immunity against antigens you have encountered previously — which brings us to the next topic, vaccines.

How do vaccines work?

Vaccines are hardly a new concept to most people alive today; vaccines against COVID-19 are being rolled out across the world, with tons of publicity. But how do they work?

This is where it gets interesting. Your immune system does not have to encounter the pathogen (the whole virus) to learn how to create antibodies to defend against it; it is enough to introduce the antigen (the protein spikes). This is the part of the virus the immune system reacts to and what antibodies attach to.

Put simply, then, the idea behind a vaccine is to isolate the protein spikes of a virus, then introduce these spikes to the immune system. By doing so, there is no chance of the virus replicating in the vaccinated person’s body, as there is no DNA/RNA to orchestrate the replication process. That’s how vaccines are both safe and effective.

Now that we know the basic goal of a vaccine, let’s explore the different strategies we can use to get there.

Traditional Vaccines vs. mRNA Vaccines

Traditional Vaccines

Let’s start with traditional vaccines, which follow the most straight forward path.

Their production looks something like this:

1. Get ahold of a sample of the virus.

2. Grow more of the virus. The amount of virus to be grown is determined by the demand for vaccine doses. A lot of virus has to be grown in order to vaccinate a lot of people. Typically, the virus is injected into eggs, where it has all the stuff necessary to replicate. The US government actually keeps a lot of chickens — on farms all around the country — dedicated to laying eggs for making vaccines (if you are interested, check out this short podcast on the subject).

3. Inactivate the virus, so it won’t replicate any further from this point on.

4. Isolate the antigen.

5. Introduce the antigen to the immune system of people through a vaccine.

mRNA Vaccines

The mRNA vaccine pursues a different route which requires a bit more sophisticated methods, but ultimately simplifies the production and logistics of the vaccine.

An mRNA vaccine is produced as such:

1. Get ahold of a sample of the virus — it’s hard to get by without this step.

2. Sequence the virus genome and isolate the part of the “blueprint” that encodes the information about how to create the protein spikes.

3. Use the information from the previous step to copy that portion of the genome as many times as necessary (depending on demand) and introduce it to the immune system of people through a vaccine.

Key differences

There are some key differences between the two. Obviously, traditional vaccines require far more eggs, but there is more to take away than that:

  • You can distribute mRNA vaccines faster and further than the traditional variety. Think of sending a physical package (traditional) vs. sending an email (mRNA).
    • Once a traditional vaccine is formulated, samples of the virus have to be transported (by plane, train, boat, etc) to production facilities across the globe. Then, you have to grow more of it. All of this takes time.
    • One of the coolest traits of an mRNA vaccine is that once the genome has been sequenced and the recipe for the protein spike (the antigen) has been determined, the recipe can be sent to labs across the globe instantaneously. From there, the labs can replicate the antigen as many times as needed, using ingredients they already have available.
  • For traditional vaccines, the virus needs to be kept alive and is even actively grown; for mRNA vaccines, the virus itself is only necessary until you have sequenced it. Traditional vaccines are still produced in a very safe manner, but when you don’t need to keep the virus alive for production purposes, there is even less risk of accidental contamination or loss of control.
  • Finally, there is the potential of damaging the protein spikes through traditional vaccines. As we neutralize and take apart the virus to isolate the spikes, there is a chance that some of them get damaged, rendering the resulting vaccine less effective. The mRNA vaccines simply provide the blueprint for constructing the spikes — relying on your cells to do the rest. Thus, the spikes are made brand new every time and bear the closest resemblance to the spikes on the virus you might encounter later on. The result: a more effective immune response (a.k.a. a better vaccine).

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