If you google "How long does the flu shot last" you will be told it lasts 6 months. Yet someone from the CDC says you are protected even if you get the shot early. If I got the flu shot in Aug or Sept, per the 6 month rule, I would not be protected during the peak months.
So if there is a good match between the flu vaccine and the prevalent virus, you should be protected. However over time the virus is mutating and may no longer be effected by the vaccine.
Therefore it is not that the vaccine stops working after 6 months, it is that the virus may have mutated over 6 months. It takes many months to create the flu vaccine and if they get it wrong, as has happened in the past, there is no quick fix to get another vaccine on the market.
Remember when H1N1 was around in September 8-10 years ago? It was prior to regular flu season and none of the vaccines in the market protected against it. Both my teens got it and were sick for almost 2 weeks.
People should get vaccinated. The earlier the better. We get vaccinated by the first week in September.
That "mini illness" you describe is a good thing. It's a sign that the vaccination worked. Contrary to popular misconception, you can't get the flu from a flu shot. It's a deactivated virus. You can get symptoms that mimic those of a cold or flu. That's your immune system responding to the vaccination. Which is the point of a vaccination. To fool your immune system into producing a response so that when it does encounter the actual virus, it's ready to deal with it.
The CDC is working on flu shot cocktails for 2020 right NOW--it's a total crapshoot--they are guessing at what strains of flu may be hitting NEXT YEAR.
But getting the flu shot is a good idea, and had I an immune system in my body I would be getting one. And I can and might get one in APRIL. Right now I am relying on 'herd safety' to keep me from catching flu. (She said as she packed for a 4 hr flight tomorrow).
The doc didn't deny me the shot, but he said it would be completely useless at this stage of the game. I definitely don't want flu, after what I've been through, but it is what it is. I'll be careful and probably bathe in hand sanitizer.
6 months is the length of time a flu shot lasts. Give or take.
NOT touching our eye, nose and mouth is always a good idea. Mucous membranes are so thin----
I AM going to get a shot in December, but for the most part, not much I can do this winter.
CVS pharmacy has the 'get your fly vaccines' signs down for about a month. Obviously, if you wanted your flu vaccine in August, you could still get it.