Latest instance; the flu vaccine people my age are urged to get doesn't work against the major strains of influenza around this winter. I've heard numbers of 30% effectiveness in the US, though I'm not sure I believe them. In the UK, it's more like 3%. The BBC says, with classic understatement:
This is a poor resultNo shit, Sherlock.
The vaccine mix used for the current season was based on a recommendation made by the World Health Organization last February, based on the breakdown of strains in the population of each country even earlier than that. It's a guess at the current flu season, in other words. The FDA appreoved the mix on February 28, 2014. Dozens of generations of flu viruses have lived, multiplied, died, and been subject to natural selection since then. Six companies make the vaccines March through August, before switching to the Southern Hemisphere.
In actual fact, it really only takes a few days to make the vaccine by the conventional route, and less using a recently approved cell-free system. The rest of the delay is regulatory; each batch has to be approved by the FDA. Shipping of some lots began in July.
It is not clear how long the FDA lot approval process takes, but it's clear the entire process is taking too long.