It doesn't need to be completely effective on an individual level if enough people get it on a societal level.

> Got my flu shot last year, still ended up with severe flu in February. The flu shot is not completely effective.

My understanding is that the 'flu shot' changes every year, in anticipation of the strains predicted to be the most prevalent that year.

In other words, flu shot producers say "we think flu strains A, B, and C will spread this year" and strains B, C, and D may be what actually spread.

It's still worth getting because even if you catch strain D, your immune system still easily defeated B and C when exposed and you didn't even notice.

The flu shot doesn't protect you from all / any flu.

Without some serious testing you're not likely to know what you got.

But even if we assume you did catch the flu, there have been long term effects that show that regular flu shots over a few years lessens the severity, occurrences of serious problems with the flu. So the benefits seem to go beyond a given vaccine.

With flu vaccines there seems to be both a specific benefit, but also more general benefit longer term.

Literally nobody said it's completely effective.

In fact, if you read the experts, you'll see the the flu shot is generally a cocktail against the most prevalent strains. Since strains are left out, it's absolutely known that the flu shot will not protect you against all influenza strains.

See this page for information on how strains are selected: https://www.cdc.gov/flu/prevent/vaccine-selection.htm

The flu shot is not a magical guarantee that you personally won't get the flu. What it does do is lower the rate of transmission for the flu significantly, by improving the herd immunity.

People need to understand that getting the flu shot is less about helping yourself, and more about helping your community. Think of it like giving blood. It's an altruistic action that you can take to help others around you.

True, but if everyone that _could_ get their shot did, it would be a lot less impactful to everyone.

Nobody is saying it is completely effective.

Its about 40% effective. Probably helped you not get the flu twice. So worth it?

Its effectiveness has on average been less than 50% in the past decades, sometimes far lower. There's just too many strains and to much seasonal variability.

But they usually also decrease the severity of the symptoms, even when they don't completely block them. This is almost as important as the full effectiveness as helps decreases death and hospital time.

Wonder what it would have been like _without_ the shot.

AFAIK, the flu vaccine doesn't prevent against all strains, because the virus mutates so rapidly year by year. They prepare it every year based on the worst/most common strains that were seen in opposite hemisphere's flu season. It does help limit the spread though, and is still really important to get.

Maybe you didn't get the flu. Flu like symptoms are very common in a huge variety of ailments.

Vaccinations are very effective protective measures. Just not at protecting against stuff that isn't in their narrow scope.

Vaccinations are very much like a blacklist (or signature-based anti-virus). They are generally highly effective against what's on the list, but they don't interact with stuff that isn't on it. Of course, some vaccines work better than others. Additionally, most vaccinations, and all the common ones, are very safe. So even though e.g. the flu shot is not 100 % effective in preventing the flu², it is practically 100 % safe, which means your expected outcome can only improve by taking it.

² I believe the actual numbers are something like 80 % for the flu: people vaccinated against flu strain X only contract it at 20 % the rate of unvaccinated people, or numbers to that effect

There are different strains of the flu and doctors sort of guess each year which strain to vaccinate for, seems like they guessed wrong in your case.