Immunology is a rapidly developing science, but it still isn’t well-known or well-understood. And it shows, especially in science fiction. Time travelers and aliens easily adjust to life on present-day Earth without the need for vaccinations. Humans explore unknown planets with breathable atmospheres without any protection from the millions of potentially disease-causing microbes all around them. Or they willingly remove what protection they have…*cough*Prometheus*cough*. It’s practically a tautology; an atmosphere that can support life is a safe atmosphere for humanoids to breathe. H. G. Wells more accurately portrayed the consequences of making this assumption in War of the Worlds. When the invading aliens were exposed to Earth’s atmosphere, they were eventually killed off by microbial infections.
This glaring oversight is sort of understandable, though. Immunology, the study of the immune system, is a relatively new field of science. The germ theory of disease wasn’t even validated until the late 19th century. Antibodies, complex proteins that enable the immune system to adapt to and remember past infections so that you generally don’t get sick again from the same thing, weren’t fully characterized until the 1960s. Gerald Edelman, Joseph Gally and Rodney Porter won a Nobel Prize for finally putting the pieces together. It was sort of a big deal.
If there is any life in an alien environment, there will be microbes. Higher forms of life may show up as well, but microbes are a guarantee if we are assuming that life is involved. If these microbes are from an alien environment, then every single one of them could be completely foreign to your immune system. There are a couple of different ways this could play out.
Microbes that cause disease generally do so entirely by accident. A survival mechanism of the invading organism just happens to interact with your bodily systems in such a way as to cause sickness or death. This is why our ability to recognize something as ‘foreign’ and get rid of it quickly is so important. Immune cells ‘see’ microbes by recognizing proteins or structures that are microbe-specific, either through specialized receptors, antibodies or other immune proteins. Given that your immune system is being exposed to something it has never encountered before, it may be entirely unable to recognize these new microbes as microbes. This would basically mean that you would be defenseless against any incidentally lethal effects they might have on your cells.
Some of the mechanisms humans have evolved for dealing with foreign microbes are particularly unpleasant. The symptoms you experience when you have a cold or the flu, for example, are actually caused by your immune system trying to rid your body of the virus. The additional mucus protects your vulnerable membranes. The increase in body temperature makes for an inhospitable environment to viral replication. Your cells that are already infected are targeted and destroyed to prevent the spread of infection. The immune response, if activated strongly enough, has the potential to kill you outright…as those with severe allergies are well aware. The prospect that your immune system would respond to foreign microbes on an alien world is at least as terrifying as it not responding at all.
Of course, it is also entirely possible that nothing would happen at all. Whatever microbes that developed on this hypothetical planet may not be able to survive inside of a human body. They may not have the potential to negatively affect human cells while simultaneously being alien enough that the immune system doesn’t recognize them. The point is that whenever someone breathes in an alien atmosphere they are taking a serious risk, and that risk is often ignored or glossed over in science fiction.
This problem applies even more strongly to human time travelers, who are already susceptible to human diseases but simply do not have the immunity or the vaccinations to protect them against the latest strain of measles or influenza. They could also introduce diseases from their own time, like smallpox or multi-drug resistant bacteria, which present-day Earth is poorly equipped to deal with. The results could be devastating.
Humans are bacteria factories. Our mouths, guts and skin are absolutely coated with microbes. Our immune system has been adapting to all of these microbes since we were born and recognizes them as ‘normal’ rather than foreign. They generally don’t cause disease unless something goes wrong. In fact, we would quite literally die without them. But introducing our normal bacteria into a foreign environment could have disastrous consequences, and I’m pretty sure that accidentally causing a plague or wiping out the local population would violate the prime directive as well as significantly alter the course of history.
I am not suggesting that any piece of science fiction will receive a fail for *gasp* scientific inaccuracy if it doesn’t acknowledge the immunological implications of every decision being made. Requiring exposition describing vaccinations or atmospheric safety precautions would be boring and honestly irrelevant in many cases. But sometimes it is relevant and could really add something to the story. Good science fiction makes you think…about the future, and about how we might deal with extraordinary circumstances. Even if most people don’t know how their immune system works, disease is something that we all know and fear. Acknowledging the risk of personal contamination or plague in the right context creates character anxiety and drama because it is instantly relatable, even in an alien environment.
The absurd complexity of the immune system itself, combined with the infinite variety of microbial life, makes for a well-spring of potential creativity. You can’t remove microbes from the picture. They are part of us, and they will be a part of any ecosystem that supports life. These are obstacles that humanity will have to overcome if we ever hope to explore new worlds. What better way to inspire their solutions than through science fiction?