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In a TV series I've been watching The Last Ship, - spoiler alert - a scientist develops a cure for himself for a virus, but actually continues to remain a carrier, and sort of weaponizes the virus accidentally, killing 3 billion people. In response, another scientist develops a cure for that virus, a vaccine, and eventually makes that contagious by close contact as well, based on data gathered from the lungs of the scientist that infected/vaccinated himself with the weaponized version.

The science behind this might be totally ridiculous, or potentially realistic / possible I don't know. Is this possible? Can a vaccine / cure to a virus be engineered into a contagious version, to cure everyone in a chain reaction?

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  • $\begingroup$ Cure or prevention? There are several vaccines that can and do spread, such as the smallpox vaccine (vaccinia) $\endgroup$ – iayork May 18 '16 at 18:06
  • $\begingroup$ Arrived at this question looking for the same thing, though from a different TV show - Doctor Who, S02E01, New Earth, in which the doctor cures thousands of infected humans by disinfecting a few, and getting those few to pass the "cure" on. The way it was actually done was ridiculously unrealistic, but raised an interesting question for me. $\endgroup$ – Hashim Apr 10 '17 at 2:03
  • $\begingroup$ There's also this, very directly related to your question: geneticliteracyproject.org/2015/10/19/… $\endgroup$ – Hashim Apr 10 '17 at 2:09
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Fun question!

I think that to make a transmissable ("contagious") antiviral vector, you would need to design a virus that can infect people and that codes for something like an antiviral drug compound, which targets specific viral proteins.

As easy as that was to write down in one sentence, I think that execution would be extremely challenging.

Making the anti-virus out of another virus seems necessary to me, as there is little alternative. You would need something capable of efficiently spreading from host to host, that can generate many copies of its therapeutic payload and that is relatively simple to engineer. A virus is the only thing that I can think of that fits the bill.

You could theoretically engineer an antiviral virus that is mostly non-pathogenic to other people, although this wouldn't be perfect. Even if it didn't code for specifically pathogenic proteins, it is a foreign molecule that is likely to raise an immune response, risks integrating into an important location in the host genome and would divert cellular energy to production of its proteins and away from other cellular processes.

Say that you get this to work, that it's minimally harmful to its host and can effectively target the more pathogenic virus, against which you've designed it. What happens when the job is done? Is it still in the host body, pumping out more copies of itself and/or its antiviral proteins? If so, then it could end up causing more damage to the host in the long run, as it uses host resources to fill cells with no-longer-helpful foreign molecules.

Given more thought or time (than I have), you could probably image more ways to tweak the design of this theoretical anti-virus, but as a brief answer, I think that the above considerations can give you a quick idea of what it would take to bring this system from the realm of science fiction to that of hard science. :-)

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Can a vaccine be contagious?

Yes.

Most currently used human vaccines are not transmissible. That is to say on vaccinating one individual, the vaccine cannot infect another individual. Oral poliovirus vaccine (OPV) is an exception. OPV is a live attenuated vaccine that replicates after administration (as all live attenuated vaccines do). Unlike other live attenuated virus, the virus in OPV sheds in substantial amounts and can be transmitted from person to person. Transmission is, as with other enteroviruses, fecal-oral, via contaminated food and water, hands or fomites (see Murray Medical Microbiology, Ch 56).

Vaccine derived virus can circulate in communities for some time. This is, in some ways beneficial, because it allows for more broad vaccine coverage and improves herd immunity, but can cause problems. Vaccine derived poliovirus can revert to what we call neurovirulent poliovirus, causing what we call Vaccine Associated Paralytic Poliomyelitis. In the US, we use a formaldehyde killed inactivated poliovirus vaccine (IPV) that does not replicate and is not transmissible. It is less effective at producing an immune response, but cannot cause disease. Strategies for a global move to IPV are an active area of investigation.

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Definitely possible, assuming you have access to sci-fi technology.

Consider a virus specifically rigged to produce epitopes (the immunizer) matching pathogenic infections. It has to survive in its host while causing negligible damage and having reasonable access to the bloodstream for immune recognition.

Next, it would have to be extremely specific to a narrow type of cell preferably exposed to the air. Immediate obvious candidate cell hosts are palatal tissue cells - exposed to the air plus reasonable bloodstream access. In this case, full upper respiratory tract is largely a non-starter since it would likely cause constant allergies similar to a rhinovirus.

Minimum damage principle: the most practical approach would be a partial lysogenic cycle where the contagious "antivirus" contents stay in host cells for a limited period of time (after which the foreign DNA/RNA is programmed to destroy itself), creating copies which grow off the surface of the host cell and shed. Preferably the contagious antiviral particles would immediately deactivate themselves on entering a host cell that happens to be strapped for resources (if the concentrations of certain needed materials are insufficient, then deactivate).

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The original vaccine was the infectious disease cowpox, which elicts a good enough response from the immune system to smallpox that it effectively prevents the infected from getting smallpox. It's just not particular contagious among humans.

But it might be possible to engineer a virus which has a very mild disease course, but is antigenically similar enough to something nasty that it provides protection, and is contagious.

But delivering a medical treatment without consent is ethically dodgy.

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