I heard you say on the Dear Pandemic NG Live that the new COVID-19 vaccine candidate from Moderna is a new type of vaccine. Can you explain that?

Biology/Immunity Vaccines

A: We recently heard reports from the pharmaceutical company Moderna that they had a successful early trial of a vaccine for SARS-CoV-2.

The way this vaccine candidate works is completely different from previous vaccines that you have likely had. It’s called an mRNA vaccine.

In order to explain this, we’re going to take a deeper dive into how a vaccine prevents infections.

Basically, a vaccine works by giving your immune system the fingerprints of a particular virus in advance, so that it can respond very efficiently when it encounters that virus in the wild–and prevent it from replicating in your body (i.e., infecting you).

More specifically, all the vaccines we know and love contain little bits of the target pathogen (e.g., measles or influenza virus) that have been killed or weakened. These inactivated viral bits are called antigens. Since the virus is inactivated, it can’t actually infect you, but your immune system doesn’t know this. The antigens are recognized by your body’s immune system as a threat, and the immune system responds to keep you healthy by making specialized cells.

Video: How do vaccines work?

After your immune system has done this once for a particular virus it has a system of remembering that same *particular* threat for the next time. It stores those viral fingerprints for quick reference. This is known as the adaptive immune system. The immune system’s specific memory of that antigen allows it to respond faster and more effectively the next time you encounter the same virus. Of course, when you encounter it in the wild, the virus won’t be inactivated, so the efficiency of the immune response will (usually) keep you from getting a full-blown infection. Or it will at least reduce the severity of the infection, if it doesn’t prevent it entirely.

But there is, theoretically at least, another way to give your immune system those viral fingerprints that does not involve growing, inactivating, and then injecting you with little bits of the virus itself. An mRNA vaccine uses your own body’s cell-building structures to make the antigen. The vaccine contains genetic instructions that tell your cells to produce a protein that is shaped like the virus (but is not actually the virus). These proteins are then recognized as foreign by the immune system, and then the immune system responds to the perceived threat. Then, just like with conventional vaccines, the immune system stores that fingerprint for later quick ID of the real virus the next time.

mRNA vaccines have some advantages. They are way easier and faster to make because you don’t have to grow the virus, so the limitations on producing a lot of vaccine in a short time are reduced. They are also theoretically safer than conventional vaccines, since they contain no messy viral particles at all. And they have been shown in laboratory settings to be tolerated very well (i.e., not cause uncomfortable reactions).

Buuuutttt they also have some pretty serious disadvantages from the standpoint of “Malia is getting super excited about an mRNA vaccine right now.” The main one is that… we have never seen an mRNA vaccine approved and gone to market before.

Not because one couldn’t be approved, but because it’s a new technology and it has just never gotten across the finish line yet. That said, my very favorite word in the whole world is “yet,” and if there was ever a moment for innovation, it’s now.

Other challenges for mRNA vaccines generally:

– We have no evidence of the long-term effectiveness of an mRNA vaccine (because no one has really studied one over the long-term).

– There are still question marks about unexpected immune system responses. These vaccines have been in smaller trials in humans, but never used population-wide where we would have a huge number of people to study. Rare side effects are a question mark.

– mRNA vaccines have to be refrigerated, which means they’re really hard to scale up worldwide. Our best bet at COVID-19 *eradication* would be getting a vaccine out worldwide, so if we end up with an mRNA vaccine, we’re making that goal hard to achieve.

And that Moderna trial? Well folks, it is early days. Vaccines go through many trials before they are released to the public, and what Moderna released was a Phase I trial (yes that is the first phase of many) with just 8 subjects. Also, they didn’t publish their results–just a press release saying that it worked.

I’m glad that it worked, here’s a little reality check. We need to *plan on* outbreak control measures for the foreseeable future. I think a vaccine will be available at some point, but not as soon as we are all hoping.

Nerdy Girl Dr. Leininger also covered much of this same vaccine development territory in her excellent previous post.

Link to original FB post