Flu shot



A flu shot is a vaccine to prevent or lessen the effects of infection with the influenza virus. New vaccines are made available every year via the health care and disease control branches of one's government, like the CDC in the United States. Generally, these vaccines are pasteurized versions of the original viruses themselves. The body then creates antibodies from these templates that it circulates indefinitely.

Fun with flu
Flu shots are also a great topic to bring up in arguments with fools who don't believe in evolution because it's precisely due to evolution that the CDC releases a new round of flu vaccines yearly. One could call a creationist a hypocrite if said creationist has had more than one flu vaccine. This is generally not a good idea, since most of these nincompoops would rather forgo reasonable medicine (like flu shots) than be called a hypocrite, so this argument is best to be used as a last resort... or as mockery. Be warned — you will be charged with gotcha arguments if this is used on more than one quack. Doonesbury sums this up quite well, although the exact context of the comic was about bacteria and their resistance.

Effectiveness
Influenza vaccination differs slightly from other vaccinations. Usually, vaccinations have exceptionally high effectiveness rates. The prevalence of the influenza virus and its many strains (as well as seasonal variants) make influenza vaccination quite unique. Although the goal of a vaccination program, of course, is not the prevention of disease in any one person, but rather herd immunity, which is accomplished with a high vaccination rate. Overall, the vaccine is effective, as flu vaccination lessens the risk of flu by between 40 to 60 percent during flu season. For instance, during the 2019-2020 flu season, over 7 million illnesses, 3 million medical visits, 100,000 hospitalizations, and 6,000 deaths were avoided solely due to vaccination in the United States.

Side effects
When you take the jab, common side effects include soreness, swelling, redness, nausea, headaches, muscle aches, fevers, and periodically, fainting. These are mild side effects, and they are the most common. Severe side effects (such as paleness and wheezing) can occur, but they are extremely rare, and most happen a few minutes or hours after injection. The vaccine is still totally safe, so these side effects aren't something you should worry about.