Here are two facts that one clearly admit and and almost read everywhere:

Fact 1) it needs many years to elaborate a vaccine (from research, creation, testing and approval)

Fact 2) new vaccine for flu influenza are elaborated twice a year...

I am sure that you understand that is non consistent. So i certainly am missing something here...

Alternative questioning:

-does it mean no efficiency test are realized for flu?

-does it mean seasonal flu is actually the same virus? (in that case it would not be advised to do yearly vaccination, right?)

-is this something else i am totally missing out?

Thanks for explanations


The paradox you describe is resolved if you think about the influenza vaccine that is approved as a procedure for making an annual vaccine. It is the procedure, repeated year-after-year, that has been tested safe and effective against the strains included in the vaccine that year.

The vaccine is produced in the same way each year, and all the manufacturing procedures are exactly the same, all that differs is which strains of influenza virus are used to inoculate the eggs (or in cell culture). These strains differ from each other, yes, but they are sufficiently similar that the vaccine works whichever strains are used (at least it is protective against those strains).

Even though the vaccine itself is therefore a bit different each year, it is not re-tested for safety and efficacy the same way a novel vaccine would be (though there are constant surveillance studies of influenza vaccines, just like other approved drugs and vaccines).

Not the answer you're looking for? Browse other questions tagged or ask your own question.