I got the flu shot last week. I got the flu this week.
First, it takes about two weeks after getting the vaccine for your body to build up enough antibodies to protect against the flu. That’s why it is recommended to get it early in the Fall before influenza is widely circulating. So, it is possible to get influenza after getting a flu shot but before you’ve built up antibodies.
Next, in some years the vaccine is a better match for the dominate strains and subvariants than in others. This because the vaccine in the northern hemisphere is developed by determining the dominate strains in the southern hemisphere. But that is no guarantee. However even if not a perfect match, the influenza vaccine may still provide some protection against genetically similar strains and subvariants and reduce the severity, i.e., complications and hospitalizations among the most vulnerable.
Finally, people often confuse common colds with influenza. While some symptoms overlap, there are considerable differences.
https://www.webmd.com/cold-and-flu/flu-cold-symptoms
A common cold may make you feel miserable for a few days – sore scratchy throat, sneezing and a runny nose, low grade fever, sometimes a dull headache and mild body aches and you may even miss a day or two of work, but influenza is very different.
The last time I had influenza I had a high fever for days, bone breaking body aches (it literally felt like someone had taken a hammer to all my joints), a pounding headache, fatigue so bad I could hardly get out of bed for nearly a week and was still weak and fatigued for another, little appetite, and a deep chest rattling cough that made my ribs sore, was off from work for well over a week.
Colds come on gradually; you feel a bit of a scratch in the back of your throat, an itchiness in your nose for a day or two, then a day or two later a sore throat and runny and sneezy nose, etc., but influenza hits you like a mac truck.
The last time I had the flu in January of 2000, I woke up feeling fine but very tired as if I hadn’t slept at all but no other symptoms. So, I showered, dressed, had a cup of coffee, ate a bagel and went to work, and got there at my usual 7:00 AM.
By the time I got to work, I couldn’t get warm, felt chilled and achy. My boss came by my desk at around 8AM to say good morning and asked if I was OK. He noticed I looked a bit pale. I told him I was just cold.
Not long after my throat started becoming very sore, like I had swallowed razor blades sore, and I suddenly became nauseated (not a typical flu symptom in adults but not unheard of). I ran to the bathroom and threw up several times. A co-worker found me in the bathroom retching and told my boss and my boss sent me home.
I barely remembered the drive home as I was now feverish and out of sorts. When I got home, I got into my PJ’s and decided to lay on the living room couch with many blankets and pillows as it was closer to the kitchen so I could get ice water and actually closer to a bathroom as I was still vomiting and now had some diarrhea (again not as common in adults but not unheard of with severe influenza) and it was the only room with a TV and a phone and a bit warmer than upstairs and I didn’t feel well enough to climb up and down the steps to the bedroom.
I called my husband to let him know I was home sick and asked him to bring home some ginger ale and canned chicken soup and Tylonol on his way home.
When he got home at around 6PM, he was concerned enough to suggest I go to the ER not only because of the high fever but also because of the deep rattling cough I now had. I had gone from feeling a bit tired but OK at 6AM that morning to 6PM that same day feeling like I was dying.
I didn’t want to go the ER and wanted to tough it out. And I did. But as I said it took around 2 weeks until I was 100% better.
I called my boss the next day to let him know I wasn’t coming in and he told me that nearly half of the office was now out sick with it too. That’s not what happens with common colds.
Lastly, I would also mention that I’ve had some people tell me they came down with the “flu, “the “stomach” flu” but that is not influenza but viral gastroenteritis or even food poisoning.
https://www.mayoclinic.org/diseases-conditions/viral-gastroenteritis/symptoms-causes/syc-20378847