Flu shots are made up of what they think the next major strains will be, however they are wrong a majority of the time. Why do we still get them? Full disclosure, I still get them.
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A few things:
1. They are right the majority of the time
2. Modern flu vaccines target multiple variants, so if they guess wrong on one, you’ve still got protection against the others
3. This is a self selecting bias: it’s more that sometimes a strain gets missed; the others still exist and would have spread more without the vaccine
4. Because the vaccines are multivalent, they create a much more robust immune response in most people
5. vaccines are not binary — you become more protected with a vaccine.
Flu shots are our best statistical guess at what the circulating strains will be this year. They typically contain antigens (recognisable virus shapes) for four different types of flu, so that our immune systems can learn them ahead of time and be protected.
Best case, the statistical guess works out and we have a quiet year, with lots of people gaining solid protection from those types of flu.
Worst case there is a circulating strain which *doesn’t* match the ones in the shot, in which case more people get the flu. Even in that case, however, if the circulating strain is anywhere close to the one in the vaccine the immune system can still partially recognise and target it, reducing severity.
> they are wrong a majority of the time
The flu is not one thing. There are many different strains (variants) the influenza virus that causes the flu, and, because it is a virus that evolves rapidly, new strains are always emerging and being discovered. This makes predicting which strains will be spread broadly among a population challenging.
While a particular year’s annual flu vaccine is not going to protect you against *all* the strains of influenza or be a 100% guarantee that you won’t get the flu *at all*, it reduces your chances significantly by providing you immunity to some, but probably not all, strains.
If you look at [the data provided by the US Center for Disease Control](https://www.cdc.gov/flu/vaccines-work/vaccineeffect.htm), getting an annual flu shot reduces your chance of getting the flu **by 40-60%** depending on a number a factors included age and health. Probably more importantly, even if you do get infected with the influenza virus, being vaccinated have been empirically show to reduce the severity of infections, number of hospitalizations, and number of deaths in the population. In summary: your chances are better with a vaccine than without.
> Why do we still get them?
1/ Because expecting any vaccine to be 100% effective is ignorant and misinformed. A 40-60% reduction in risk is fantastic and, for many people, life-saving. Especially for a virus that mutates as frequently as influenza. You get them because the risk is extremely low (you’re at more risk of death or injury just driving to work every day), and the potential upside is, you know … *not dying*. That’s a pretty good return on investment. Vaccination is a way to protect yourself.
2/ The purpose of a vaccine is not to eradicate a disease *by the vaccine.* Rather, the purpose of a vaccine is to increase a population’s immunity to a disease in order to decrease the spread of a disease. Your immunity to strain *x* of a virus means that you won’t spread (or will spread less) of that virus to more vulnerable people. Vaccination is a way to protect others.
They are not wrong most of the time as they have 4 strains in the shot and at least 1 of them is a major strain that year, they might not always pick the top 4 though.
But that doesn’t matter as the immune system does something really cool called [__affinity maturation__](https://en.m.wikipedia.org/wiki/Affinity_maturation) where over time/exposure to a pathogen the immune system can get better at recognizing it. It’s a lot faster to slightly modify immunity from one flu strain to a slightly different one than it is to build it up from scratch. Not to mention there is usually some cross immunity between flu strains anyway.
Lastly, there is now some evidence that people that get the flu shot have lower rates of dementia than people that don’t. This could just be a coincidence, but considering flu can infect the brain and the vaccine makes flu illness less severe, regardless of the strain, this is plausible.
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