Kyle: Dr. Patrick, I've heard some people say that the vaccines themselves might be contributing to putting certain pressures on the SARS-CoV-2 virus, specifically this idea that the vaccines can make the virus actually more deadly or more virulent. What are your thoughts on that?

Dr. Patrick: I certainly like coming into hearing these statements, which I've heard and it's proliferated on many different areas of the blogosphere and people that...you know, friends of friends, you know, etc. My first thought was, well, if this is...we need to know whether or not this is true because, if it is, it changes everything in a way, right? You don't want to make a virus, you know, more deadly to the unvaccinated. And that's kind of what the general statement is, is that vaccines are causing selective pressure for the virus to mutate into a more virulent form, which is more dangerous and deadly to the unvaccinated. Nobody wants that. Like if that were the case, I mean, all of our children are unvaccinated. So, you know, as a parent, to me, I wanted to get to the bottom of this and understand, is this something to be concerned about because, if it is, it's a game changer in my mind. So, as a non-evolutionary biologist, I went on a path to trying to understand to the best of my knowledge, you know, the literature and what the literature out there says on how viruses evolve and what the selective pressure is and, you know, what that typically, you know, entails. And so from all of my reading and understanding, again, I'm not an evolutionary biologist, to me, I came out of it with the understanding that viruses...the selective pressure on viruses is to evolve to become more transmissible. They are not under a selection pressure to become more virulent. In other words, it's not in their best interest to kill their host because, if they kill their host, then their host can't incubate the virus and allow them to reproduce and infect more people. And so all the studies that I've read outlined that there's these factors and that virulence isn't something that's selected for. It is something that happens incidentally to transmission. In other words, it sort of hitchhikes alongside. So, a virus evolves to become more transmissible, like that is its major purpose. And in some cases, if it becomes more transmissible, sometimes it can also become more virulent. It can be more, you know, dangerous to its host.

So many of the different studies have outlined that there are factors that limit transmission. So, if something limits the transmission, then it's also going to limit the potential of the virus to become more virulent. And the factors that limit transmission are, one, physical constraints. So, the virus infects human cells, and the human cells then make viral proteins, and, you know, are basically allowing the virus to replicate. So, our own cellular machinery, the ability of our cells to assemble viral proteins, the ability of ourselves metabolically to do it quick enough, like there's a limit to that. Like we can only do that so quickly. So once that happens, then, you know, a virus has sort of reached its peak transmissibility in a way because our cells physically can't do it quicker than it's already doing it, if that makes sense. And so with the Delta variant right now, we may be at a peak transmissible...you know, we may be at the point where our cells can't assemble all the viral proteins quick enough for it to become even more transmissible. We don't know. Maybe we're not there yet, but maybe we are. We have no idea. It's definitely a much more transmissible variant. So that's the one thing that limits the ability of a virus to become more virulent is the limitation on transmission.

The other thing is host mortality. If a virus is killing the host within a certain time frame before transmission ends, then, you know, you start to like not be able to transmit the virus more, and you're not going to have more variants crop up because the host is dying. And so this is something people have been very concerned about with vaccines because the argument is that vaccines are preventing more...they're preventing people from dying from COVID-19, and therefore, they're going to allow the virus to have a chance to mutate into something that is more virulent. Again, it has to mutate into something that's more transmissible, virulent hitchhikers alongside of that. But if you look at the deaths in COVID-19, people that are unvaccinated, or just generally speaking, people usually die much later than the transmission phase. They die, you know, days and days and days after actually becoming infected with SARS-CoV-2. And so the transmission phase is well over before people are even dying. The reality is, is that people that are unvaccinated have...they're creating these mutations and allowing variants to evolve even at a greater rate because, not only are they, you know, able to do it even before they potentially succumb to death, but, you know, the fact that we just talked about overall transmission reduced by vaccine, so, people that are vaccinated are less likely to even get infected, and we talked about onward transmission reduced, in other words, people are clearing the virus faster that are vaccinated than unvaccinated. In every sense, people that are unvaccinated, there's more chances for the virus to replicate and to potentially mutate and form another variant that could become more transmissible, and that's potentially more virulent.

Now, people are also conflating the vaccine escaped immunity. That is a completely different thing. That is not something that is relevant to virulence, if you look at the large body of scientific literature covering this topic. I shouldn't say large body. It's actually quite limited. So there's no example of human vaccines causing a more virulent strain. There are examples of vaccine escape. So in other words, variants crop up that are no longer...that can evade the antibodies produced by vaccines. That's a different thing. That isn't something that's more virulent. That's something that's going to affect people that are vaccinated because now they're going to be more likely to be infected, and their vaccine is less effective. That's a very different thing than what we're talking about, which is the evolution, the selective pressure on viruses to transmit, become more transmissible. And that is the selective pressure that exists, not virulence. Virulence hitchhikes alongside the transmission aspect of why viruses, you know, mutate basically in the selective pressure that's on them to do that.