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Penn State Researcher Says Vaccine-Driven Virus Evolution In Chickens Shouldn't Discourage COVID-19 Vaccination

Penn State biologist Andrew Read (right) and research assistant Chris Cairns studied Marek’s disease virus in chickens.
A Chan
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Penn State biologist Andrew Read (right) and research assistant Chris Cairns studied Marek’s disease virus in chickens.

A research paper published in 2015 showed vaccines could enable more deadly variants of a virus to spread among chickens.

Penn State researcher Dr. Andrew Read, who led the study, said the paper has gone viral in recent weeks because readers are misunderstanding it and making unfounded comparisons with COVID-19 vaccines.

Read studies the evolution of infectious disease and is the director of Penn State’s Huck Institutes of the Life Sciences. WPSU’s Min Xian talked with him.

Here's their conversation:

Min Xian: Andrew Read, thank you for talking with me.

Andrew Read: My pleasure.

Min Xian: The 2015 research that you led showed that vaccinating chickens against Merricks disease allowed the spread of more deadly variants of that virus, which would not have happened without vaccines.

Andrew Read: That's right. In the chicken virus, there are variants, which are extremely lethal to unvaccinated chickens. And in fact, they can kill the chickens before the chickens have begun to transmit the virus. In other words, the 10 days or so it takes for the virus to become infectious, the chickens are dying in that time. And so the vaccinations of the chickens keeps those chickens alive, stops them dying. And so therefore, those variants can transmit onto other birds.

We were doing that work because we're very interested in the sort of scenario where that could happen. And it was well understood that vaccines had failed in that virus before we started working on it. But the actual reasons for it, and how it’d come to be that the evolution took the path that did, that was not so clear. And so the key part of our paper was looking at how the vaccines are acting on these different variants, when the different variants have an advantage and can spread in the population, and when they can't do.

I'd say, too, the other thing about the paper is that we were dealing with the first generation vaccine that was used in those chickens. So it was introduced around 1970. And it worked for about 10 years, and since been replaced by other vaccines. Those other vaccines, particularly the third generation vaccine, stopped all of the virus evolution, there's not been vaccine breaks since the third generation vaccine came along.

Min Xian: The paper has gone viral in recent weeks, it was viewed hundreds of thousands of times and, you say, misinterpreted because some people are drawing comparisons in the context of COVID-19 vaccines and the growing number of COVID-19 variants. What compelled you to write about it?

Andrew Read: I was getting emails from people who were saying that they were choosing not to take the vaccine because of my paper. And there was a lot of people out there pushing it as a reason to stop global vaccination in general. And so from my point of view, there's a major misinterpretation of the paper and there was a very, actually quite frightening experience. And there were doctors writing to me saying, can you write something I can point people to to say this is not a reason to avoid vaccination. And it really is quite amazing to me that the work on the long term evolution of a virus would be used to argue against vaccination now, when these vaccines are clearly life saving, and they're clearly making a huge difference to many, many people. And that was what really got me engaged in writing for the public on this topic.

Min Xian: And I want to say it's fair to say that you don't think that comparison is fair.

Andrew Read: That's right. I think there's no argument for withholding life saving vaccines right now. The way that the thing -- the virus might evolve in the future is absolutely something we need to think about and be concerned about. But it is not a reason for avoiding vaccination now. And I think that was the, to me, the most disturbing thing about how people were using the paper.

Vaccine driven evolution has been quite rare for almost all of the human vaccines, there hasn't been any vaccine driven evolution. And in some of the agricultural situations, like with the chicken virus we're working with, there has been, but it's by and large the less likely outcome. And then if something is evolving in response to the vaccines, it can go in a variety of different directions. And so there's the direction that went in the Marek’s Disease. And there's a direction that went in and other situations where more benign variants were spreading. It's very hard to know whether you can extrapolate from one virus to the other. We know that viruses are very different in how sick they make you, you know that there's a big difference between COVID-19 and the common cold. So viruses can evolve in different directions, we need to figure out we need to watch and carefully surveil which direction this virus is going to take, if any in response to the vaccinations, we absolutely need to watch that.

So right now, we do need to take this prospect seriously. But we aren't able to predict which direction things will go if they'll go in any direction at all.

Min Xian: What are some nuances to keep in mind when we're asking that question?

Andrew Read: It's been disappointing to discover the delta is so good at transmitting on from vaccinated people, I think it's really important to say that the vaccine is still preventing many cases of infection. So even with Delta, something like two thirds of cases are prevented, the actual infection itself is stopped by the vaccination. So that vastly reduces the evolutionary potential of the thing anyway, because it's now getting into, hitting these dead ends. So it's been surprising that it can still get through some people and that does allow the potential for virus evolution through those folks, of course there's also viral evolution happening through unvaccinated individuals and through people that have had COVID and now are naturally immune. So there's a very complicated environment for this virus to evolve. And so that's an important nuance.

The other thing is that we really don't know at this point how disease severity and disease symptoms impact transmission of this virus. We don't know at the moment whether getting sick does have an impact on transmission, and what sort of impact, what sort of size and so forth.

And then I would say the final thing that's really tricky, is we don't know what it's possible for this virus to do. So what mutations can it access? What new types of virus can it become from a mutational process? And probably most of those single mutations are already out there now. But if we get recombination between different lineages, or between lineages, other viruses in SARS-COVID-2, then we could get new genetic variants popping up, but we can't know until they pop up, what's accessible to the virus from an evolutionary perspective. And that's what makes prediction extraordinarily difficult.

Min Xian: In the case of Marek’s disease, like you mentioned, the solution to the so-called imperfect vaccine was to develop more potent vaccines. Is there a lesson there for COVID-19 in terms of how infectious diseases evolve?

Andrew Read: Yes, if we could make the vaccines prevent transmission very effectively, then evolution in the vaccinated would be negligible. And that probably is something we could do with either more potent vaccines, or perhaps higher concentrations per shot, or boosters, or mixing and match between different types of vaccines, you know, the Pfizer and the Mordena, for example, and so forth. And there might be that there are other newer vaccines that we will develop in due course, like for example, once we might sniff or breathe in, that would generate an immune response in the upper respiratory tract and the knows where the transmission is coming from. So next generation vaccines or modifications to the current vaccines could really impact transmission and I think it's great these vaccines save lives, and it's really great they stop infections. Now we need to try to focus on making the transmission reduction even better.

Min Xian: Andrew Read, thank you so much for sharing with us.

Andrew Read: My pleasure.

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