2406: Viral Vector Immunity
This comic is another in a series of comics related to the COVID-19 pandemic. This comic is the third of five releases, following 2402: Into My Veins and 2404: First Thing, which reference the new COVID-19 vaccine. It was released on New Years day, without being a New Year comic. This had not happened since 2010.
The comic attempts to explain a virus vector vaccine and one way it can fail, using the story of the Trojan Horse as an analogy. Note that neither the Pfizer/BioNTech nor Moderna vaccines are virus vector vaccines, using lipid nanoparticles for delivery rather than viruses.
A vaccine is a way to familiarize a host's immune system with a pathogen without actually causing the host to fall ill. There are many types of vaccines that have been developed, all of which are ways to present a significant segment of a pathogen's molecular structure to the host body, so that the immune system recognizes the pathogen and mounts an immune response faster when a real infection happens.
A viral vector is a tool used by molecular biologists to deliver genetic materials into cells.
A viral vector vaccine, also known as a live vector vaccine, uses a modified virus, different from the pathogen being immunized against, as a carrier to deliver a molecular payload into the host body. This modified virus is called the vector because it is the method of delivery of a piece of the pathogen's genetic code. If the recipient has a strong immune response to the vector itself (i.e., the proteins making up the surface of the vector virus), the immunization may be less effective because the vector virus, and hence its payload of viral genetic material, will be destroyed before they can enter the host's cells. It is to some degree a dice roll, with regard to whether some recipients will already be immune to a vector.
For example, a modified (to be harmless) cold virus can be used to deliver genetic material (RNA or DNA) of another virus into the patient's cells. The cells are induced to manufacture protein found in the pathogenic protein, which the patient's immune system detects and reacts to. That way the immune system recognizes the pathogenic virus without actually being infected with it, which decreases the time needed to react to a real infection. Any patients whose immune systems recognize the modified cold virus (the vector), and destroy it rapidly, won't get the full intended benefit of creating a strong immune response to the second virus (the payload inside).
The comic represents this idea with the Trojan horse being the vector, carrying a payload of Greek soldiers into the cell, as represented by the City of Troy. In the original Trojan Horse story, Greek soldiers hid inside a statue of a horse which the Trojans were told was a gift to Athena; the Trojans brought it within their walls (which the Greek army had failed to penetrate in an extended siege), allowing the soldiers in the horse to undermine the city's defenses and let in the rest of their army to take the city. Note: In a viral vector vaccine, the payload inside the vector works to the benefit of the person receiving the vaccine - opposite to the soldiers inside the Trojan horse, who had only malice in mind for the city receiving the "gift" horse.
In the comic the warriors, rather than finding the wooden horse a benign object, recognize the shape of the delivery vehicle (the Trojan horse) as being similar to an animal that trampled one of their own earlier and therefore refuse it entry. An amusing point here is that they are not as such surprised at the arrival of a wooden vehicle at their doorstep, rather that its shape resembling an animal they have found threatening before, which is similar to how simple in its judgements the immune system can be. (In addition, although the warriors suggest pushing the wooden horse into a gorge, there are no gorges very close to Troy, which is situated close to the sea on the Plain of Troy.)
The title text is a further riff on this theme, playing on an advertising campaign for freeze dried coffee. In the advertisements a narrator would claim to have secretly replaced fresh brewed coffee with that made from freeze dried to see if subjects could tell the difference, the contents of the coffee cup being the payload and the narrator the virus vector. The test subject's use of a sword relates the situation back to the Trojan scenario of the panel.
- [A large wooden horse statue on wheels stands before a city wall, upon which are standing several warriors who are shouting and brandishing spears.]
- Warrior 1: Look! It's a statue of that horrible animal that trampled Steve!
- Warrior 2: Burn it!
- Warrior 3: Smash it!
- Warrior 4: Push it into the gorge!
- [Caption below the panel:]
- How vaccine failure due to viral vector immunity works
Mentioning explainxkcd on Randall's tweet https://twitter.com/xkcd/status/1345061851424501761 started off some explanations 188.8.131.52 18:09, 1 January 2021 (UTC)
Is anyone else reminded of the "Boil 'em, mash 'em, stick 'em in a stew" rhythm? "Burn it, smash it, push it into the gorge". Into breaks the rhythm a bit, but perhaps it could be a The Two Towers (Lord of the Rings) movie reference? 184.108.40.206 19:59, 1 January 2021 (UTC)
Couldn't a similar comic be used to explain how immunity works in general? Instead of the horse being a vaccine vector, it would be a pathogen, and the immune cells recognize it from a previous encounter and attack it. Vaccine vector failure occurs when the vector resembles something you've developed immunity to. Barmar (talk) 20:33, 1 January 2021 (UTC)
- Yes, I agree with this — the current explanation for the comic (Trojan horse = immunity vector, Steve-trampling horse = common pathogen) doesn't explain how viral vector immunity works, it explains how it fails to work. I think a more appropriate explanation for the comic would have the Trojan horse be the pathogen against which immunity was desired, and the Steve-trampling horse be the DNA carried by the immunity vector. This would also be consistent with the traditional use of the Trojan horse to signify an unexpected threat (as opposed to the current interpretation's, whcih has the Trojan horse be beneficial). 220.127.116.11 08:05, 2 January 2021 (UTC)
- I think you're absolutely right that the current explanation is interpreting the comic as an explanation of how viral vector immunity fails to work, while your suggested explanation interprets the comic as an explanation of how viral vector immunity works. The caption of the cartoon, "how vaccine failure due to viral vector immunity works" shows that the existing interpretation is the intended one.Yp17 (talk) 14:24, 3 January 2021 (UTC)
- I think you are misunderstood about the workings of a viral vector vaccine. The whole premise of this approach to vaccination is to use the ability of a virus to sneak into a human body undetected, later releasing its payload into the cells, but for a beneficial gain, rather than harm. The vector virus is perfectly represented by a trojan horse - it is supposed to enter the gates unrestricted. In the case of a real infection, the virus RNA injects itself into the cell and takes over its live processes, much like the soldiers took over the city after coming out of the Trojan horse. In the case of a vector vaccine, the trojan horse bears a beneficial payload inside. The trampling-horse is an incidental "immunity" to everything that looks like horses, i.e. immunity to the vector virus, not the payload virus (which they never get to experience since the horse never makes it in). 18.104.22.168 02:21, 3 January 2021 (UTC)
- I think the issue is that it's an imperfect, flawed analogy to begin with where the details and their relationships don't quite match those of the subject it is being compared to, so any attempt to accurately explain the analogy can't be perfect either.--22.214.171.124 05:28, 4 January 2021 (UTC)
- Yes, and Randall has now done just that: vaccine-triggered immunity is now explained (via Star Wars analogy) in 2425: mRNA Vaccine. DKMell (talk) 09:07, 16 February 2021 (UTC)
I would disagree with the title text explanation, at least to a degree. The narrator is the person being recognised and threatened with the sword, but the narrator is not the vehicle of delivery of the modified payload (the coffee), that would still be the cup. I think either the metaphor or the explanation breaks at this point, which is not uncharacteristic of the title text often deviating from the stricter rules of the comic. 126.96.36.199 21:30, 1 January 2021 (UTC)
- Right. The common theme is that the victim of a trick has seen through the ruse. In the title text, the narrator is the perpetrator of the coffee replacement trick, and the victim has detected the difference (or already knows about it by hearing from someone else -- similar to the way the immune system is forewarned by vaccines) and is now coming after the narrator with a sword. Barmar (talk) 06:12, 2 January 2021 (UTC)
- I don't think it's so much the victim seeing through the ruse, it's that the victim has other reasons for attacking the narrator, before even getting to the point where she would drink the coffee and possibly notice any difference, removing the whole point of the ruse without the victim realising that there was a ruse. In the case of the Trojan Horse, this other reason is Steve's previous encounter with a horse, leading them to destroy the horse statue without the Greeks inside it ever coming into play. In the case of the viral vector, the other reason is the previous immunity to the carrier virus, destroying it before the payload can be delivered into the cells. In both these cases, the "ruses" fail because of unconnected reasons the "perpetrators" didn't know about. In the case of the title text, even the reader doesn't know this unconnected reason.188.8.131.52 11:31, 3 January 2021 (UTC)
The narrator in the alt text/title text is the scientist/researcher performing the experiment. Except that the researcher doesn't usually get threatened with attack from the research subject. In some cases perhaps they should though, such as the Tuskegee experiments.
In the other comics mentioning Steve no-one liked him too much...--Gunterkoenigsmann (talk) 06:06, 4 January 2021 (UTC)
There is a huge gorge several kilometers southeast of Troy at Kemer Creek. 184.108.40.206 22:46, 10 January 2021 (UTC)