So you get a vaccine every year against the same disease?
There are over a dozen influenza strains every year. Flu shot covers the most dangerous/prevalent one.
Exactly. It's guesswork sometimes, and some years they guess wrong. But still, some immunization is better than none.
Yes and yes. Have you had the flu before? If you're not sure then probably the answer is no. It's not like a worse cold. It sucks the life right out of you and can linger for a full week. For the most part only children and elderly are at real risk but there have been specific outbreaks that have killed hundreds of millions of able-bodied adults. I believe there was one in 1918-1919 that was almost as costly in lives as WWI itself was. They called it the Spanish Flu in the US, not sure what it was called in Argentina but it was a global outbreak so likely Argentina was hit and gave it a name.
It knocks me for a loop for longer than a week. It's not just the part of it where you're in bed trying to cope with it, but afterward, not quite sick enough to have to stay in bed all the time, but still too weak and dizzy to get a lot done outside of bed. And as the years have passed, it's gotten to the point where I don't dare get the flu - I'd end up in the hospital, with a lot more sick people, where some of the nurses are pretty damn clueless and careless about doing everything by the book because they hate the paperwork, and of course there wouldn't be anyone available to take care of Maddy.
As for the Spanish flu... that's what killed my great-grandmother. She was one of the many young adults who died.

My grandmother was only 8, and my great-aunt was 13... and had to quit school to take over running the house while their father (my great-grandfather) ran the farm. There's an old picture in the photo album of my grandmother and great-uncle being sent off to school on horseback - they still had school until age 13.
I have only had it once in my life and that was enough to make me ready to take precautions to never get it again. I haven't caught it since I started getting flu shots although three weeks ago I came down with a sudden, high fever and complete exhaustion that may have been the flu. The only reason I'm not sure if it was the flu is because it passed in a day - the symptoms lined up with my previous illness, just not the length or severity.
What I have right this second is a particularly bad cold but not the flu. My nose didn't really run with the flu like it is right now, which is what always happens when I have a cold. With the flu, I just couldn't eat or move and I had a fever in the 100's for 7 complete days and ached something fierce. I lost a bunch of weight coming out of it and it was at least a couple of weeks after the illness passed before I fully recovered.
Since then I've had 5 or 6 flu shots but haven't had one yet this year. So I wonder if I did get catch the flu three weeks back but I've got some limited resistance from all the flu shots I've had since the first time I caught it.
Some strains hit people in different ways.

My sympathies, as I know how awful it feels, both during and while you're trying to recover.
Anyways, if it's not obvious by the length of this post I definitely believe it is necessary and effective to get a flu shot every year.
A flu shot once made me feel quite ill for a couple of days. Since then I've been a little hesitant in getting the shot every year. Although most often I've had little or no immune response to a flu vaccine.
Aches and dizziness for a couple of days are a normal reaction to the flu shot. A lot of people mistake that and carry on, "OMG, the flu shot gave me the flu!

" but that's not what is going on.
The rule at the flu clinics here are that once you've received the shot they want you to sit quietly for about 15 minutes
at the clinic, just in case you do have an adverse reaction that's abnormal. The last thing they want is for someone to get the shot and then faint while driving or just walking around on the street.
Yes, I've had flu, with actual muscle pain, headaches, eternal congestion and so on.
The herd immunity aspect is one I'd not considered.
This general lack of understanding of herd immunity is why fewer parents are getting kids immunized and so they end up putting other kids at risk. Next thing you know, half the classroom is sick, and some kids whose immune systems are already compromised for some other reason are put at risk of having to be hospitalized.
This doesn't just apply to the flu. Every year there are notices that anyone who was at some public location on a particular day (usually a clinic or restaurant or school) should be alert for symptoms of flu, measles, etc. and if they feel sick, consult a nurse - who will then advise them as to whether they should see a doctor. What they don't want are a bunch of people clogging up the ER when they don't need to. But of course there will be people who are really at risk who should go there.
All in all, it's simpler to just get the damn shot and be done with it. And yes, I know there are valid medical reasons why some people can't... but "because so-and-so said on the internet that it causes autism" is not a valid medical reason.
Another simple thing is paying more attention to washing one's hands. I never touch elevator buttons with bare skin if I can help it, and the first thing I do after entering the apartment is wash.