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The vaccine contains more than 50 live viri.

The “dead virus” canard has been shown to be nonsensical. Viri do not possess any property of life; they are replicated by living organisms that host them.

While it's true a virus is not "alive" as the word is typically defined, the flu vaccine is made not from "live viri". You are right to say viruses aren't alive, so it's obvious you can't be right to say "The vaccine contains more than 50 live viri".

I worked for 3 years making flu vaccine, I know how it's made. Basically, to not be too technical, the virus (a particular strain thereof, well really 2 or 3 of the suspected most common for the next year) are torn apart (via a chemical reaction) and these virus "parts" (if you will) are then put into the vaccine. These parts of the virus are what cause an immune response, conferring (at least theoretically) immunity on the recipient.

The flu vaccine is typically described as "not containing a live virus" for this reason. Because it doesn't contain a whole virus, only parts of it, again intended to cause an immune response without actually having any danger of infection. The virus "parts" that are in flu vaccine are essentially "dead' (although as you correctly state, viruses aren't ever "alive", by the strict definition of "life" typically used in biology). The point is, the flu vaccine doesn't use a whole virus particle, unlike other vaccines for other viral infections that may (the early vaccines for small pox come to mind, that used a variant of the small pox virus, but still a virus that could potentially cause infection, just a less severe infection known as cow pox).

So it's true the flu vaccine doesn't cause the flu, it can't, unless the entire biological theory of germ theory is wrong.

What most likely happened this year were probably a comedy of errors. First, the particular strains this year that were most common were probably particularly virulent. Second, the strains that ended up being the most common were probably not what was predicted the previous year when the flu vaccine for this year was being produced. So, for those reasons, the vaccine wasn't as effective as other years. It's nothing more mysterious than that.

Four types of vaccines are currently available:
Live virus vaccines use the weakened (attenuated) form of the virus. The measles, mumps, and rubella (MMR) vaccine and the varicella (chickenpox) vaccine are examples.
Killed (inactivated) vaccines are made from a protein or other small pieces taken from a virus or bacteria. The flu vaccine is an example

Imagine that.

https://medlineplus.gov/ency/article/002024.htm