2238: Flu Shot
In this comic, Megan tells Cueball that she got a flu shot, which is a vaccine commonly prescribed in the winter months to prevent getting the common flu. She then goes on to claim she doesn't have to worry about being bitten by bats, but the worry with being bitten by bats is rabies, not the flu. This implies she got the two confused and Cueball begins to correct her. But she just talks over him not listening to him. She then goes on to claim to now be immune to other conditions, such as poison ivy, snake venom, sunburn, contaminated water, and even computer viruses.
At the end of all this, Cueball has given up on her, and proclaims that he supports her attempts to test the strength of her Flu Shot.
In the title text, Cueball asks Megan how often she gets bitten by snakes and why she boils water. She answers dunno (maybe to the water part, she must at least know how often she gets bitten). She then tells that some members of the U.S. Centers for Disease Control (CDC) keeps coming to her house asking about its history and possible curses, a humorous escalation which implies that Megan's absurd exposure to various forms of harm has brought them to the point of wondering if the supernatural may be involved. (Megan may have invoked a curse on herself or her residence when she and Rob desecrated an ancient Indian burial ground and smashed up a voodoo shop in 782: Desecration.) At the end of her reply she mentions that she got the flu shot from one the CDC guys, and she is thankful for that at least. Which is logical since she expects it to protect her from literally any danger she has ever put herself in.
Explanation of "immunities"
The flu shot consists of inactivated viruses from four different strains of the flu, which are those judged by the World Health Organization (WHO) to most likely be in wide circulation in the following flu season. Because the influenza virus comes in many strains and mutates rapidly, the flu shot is generally less than 60% effective at preventing flu infections; this is a positive effect for health outcomes, but it's not exactly what most people think of as "immunity", especially compared to e.g. the 97% effectiveness of the MMR vaccine against measles, Mumps and rubella. Statistics show that flu vaccine recipients are slightly less likely to die from a variety of other causes, but this is believed to be either because someone with the flu is more likely to have a heart attack, car accident, etc., or because of the healthy user effect (i.e. people who take the time to get non-mandatory vaccines are probably also taking better-than-average care of themselves in other ways, although this is clearly not the case with Megan in this comic strip). Even if there is a slight protective effect, it will certainly not completely prevent harm from coming to Megan by the other sources of infection or poison she mentions, except to the extent that all of these things will be even worse for her if she is also sick with the flu:
- Rabies is a near invariably fatal viral disease that causes brain inflammation, which in turn causes symptoms including aggression, fear of water, and violent uncontrollable limb movements. It can be carried by almost any vertebrate animal, but bats, raccoons, and wild dogs are the stereotypical carriers. There is a rabies vaccine, but it is generally only administered to pets and to humans who work extensively with animals or travel to regions with an elevated risk of contracting rabies. The rabies vaccine is also effective to prevent rabies after exposure, but only if administered before the victim starts showing symptoms.
- Poison ivy is a vine which produces an oil, urushiol, which chemically reacts with membrane proteins on the skin cells it contacts, tricking the immune system into attacking those cells, causing an itchy, irritating rash. Some people are not affected by poison ivy, but as it is an allergic reaction, people often become more sensitive to poison ivy upon repeated exposure. There is no known vaccine or other permanent preventative treatment against urushiol sensitivity, although there are several creams that can be applied in advance of expected poison ivy exposure to reduce the risk of contacting the chemical.
- Sunburn is caused by exposing the skin to high levels of ultraviolet radiation, such as by playing outside in noontime sun for an hour or two without clothing or sunscreen. Repeatedly getting sunburned can increase the risk of skin cancer later in life, and one severe sunburn can also trigger it. As ultraviolet radiation is a form of electromagnetic energy, it cannot be prevented by vaccination, but use of sunscreen with a high SPF (sun protection factor) can provide protection for a few hours. Melanin provides some natural protection, so skin cancer occurs disproportionately in some races, although it can occur in any race. Stimulating melanin production through controlled exposure to UV radiation for cosmetic purposes is called "sun tanning", but physicians now recommend against the practice, because the UV radiation used for tanning can also cause skin cancer.
- Snake venom is not one single compound, but several proteins and molecules produced by venomous snakes to inject into prey. Different snakes' venoms have different effects, so there is no single vaccine or antivenom for all snake bites, but antivenoms are produced by a process similar to vaccination. Small doses of venom are injected into host animals, such as horses, to provoke an immune response; the resulting antibodies are then stored to be injected into snakebite victims, where they will bind up and inactivate the toxic proteins and mark them for disposal by the immune system. Antivenom is more effective the sooner it is administered; for venomous snakes in North America, it is generally recommended to be treated within six hours of being envenomated.
- Raw water may be contaminated by bacteria, protozoa, parasites, and chemical pollutants. Boiling water will typically kill off most biological contaminants, preventing water-borne diseases such as cholera, dysentery, and giardiasis. In many areas of the world (as most of the US, where xkcd is usually set), boiling water is generally not necessary due to municipal water treatment, but if those treatment facilities are impacted by a disaster or the pipes carrying the treated water experience a failure/break, the government may advise residents to boil their water before drinking it. This is likewise advised for people living or travelling in less-developed areas, like backpackers or farmers. Some of these diseases can be prevented by vaccines, but because there are so many microscopic life-forms in water, it is not possible to vaccinate against all of them. There was a brief fad in 2017-2018 of selling bottled raw water in health food shops, advertised as a "probiotic". While it is true that untreated, unfiltered spring water has more microbes in it than purified water, these microbes are not beneficial to human life and may even kill you in some cases.
- Computer viruses are computer programs that now usually spread through networks via infected devices, attachments, and websites (early computer viruses were often spread by floppy diskettes). They can cause harm directly by taking up computer cycles and network bandwidth, but nowadays they often perform other tasks for their creators, such as exfiltrating financial information or encrypting files and demanding ransom for the keys. Computer viruses can be recognized and blocked or deleted by antivirus software that scans incoming files and links against known computer virus patterns, which is analogous to vaccination, but there is no vaccine that can be administered to Megan which would protect her computer.
- Megan specifically mentions clicking on links that have "weird Unicode in them"; this may be referring to an IDN homograph attack, in which attackers register domain names that use Unicode characters that resemble ASCII characters to trick users into thinking they are visiting a website belonging to a trusted party. For example, an attacker could register a website with the URL "xkсd.com", in which the Latin letter "c" is replaced by the Cyrillic letter es (с), and then send emails to trick users into visiting that site and attempting to log in. The attacker can then attempt to use the supplied passwords on more important websites, as in 792: Password Reuse.
- [Megan is walking with bother her hands held up in fists. She talks to Cueball who replies to her from off-panel. His presence is revealed in the second panel.]
- Megan: Yesss, I got my flu shot.
- Cueball (off-panel): Nice! I got mine a few weeks ago.
- Cueball (off-panel): Immunity buddies!
- [Megan spreading her arms wide in front of Cueball.]
- Megan: Now I can finally get bitten by all the bats I want!
- Cueball: No, that's rabies, that's not what-
- [Closeup of Megan's head, with Cueball's reply coming from off-panel.]
- Megan: I'll be able to roll and play in the poison ivy without a care in the world!
- Cueball (off-panel): Why would you do that even if the shot did-
- [In a frame-less panel Megan is flexing her arms holding her fists up, she has turned partly away from Cueball who looks at her.]
- Megan: No more slathering on sunscreen. No more rushing for antivenom after a snakebite. And now I can stop wasting time boiling contaminated water before drinking it!
- [Megan is running away from Cueball, while she is holding one arm up, her hand making the like symbol with a thumbs up.]
- Megan: Gonna click on every URL in every email I get, even the ones with IP addresses and weird Unicode in them!
- Cueball: You know what, sure, go for it.
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