PT,
Technology gets faster all the time
When Mr Briggs &Mr Stratton started to make engines the only way to test a new engine design was to make a set of drawings , send then down to the foundry & machine shop hen 10 days latter you had a test machine.
Now days I can sit at my computer , design an engine, build it virtually and run it on the desktop .
I can change the bore, stroke, piston ring width, ring placement , gudgeon pin placement even the size & position of the cooling fins, all on the computer without touching a single piece of metal .
The same technology exists for medacines.
W can thank Thalidomide and in particularly AIDS for that where they made softwear to check what almost every combination of currently available drugs in every doseage levels before they gave it to a single patient .
Microscopy has gone leaps & bounds so researchers can see what they are looking at and watch what happens to virus packets when expose to various drugs in real time .
So before they even think of doing trials the pharmacology companies have a list of rugs that will work.
Some will kill the virus packets, some will envelope the packet and render it useless, some will stop it reproducing some will stop your immune system attacking it ( which is why you actually die ) and some will stop you spreading it .
Then the hard slog starts because if a drug has no side effects then it is not working and there are a lot of things you can not model for so that is where the clinical trials come in.
Ideally you would do this for several years to cover all of the variables ( remember those known unknowns ) and that is the bit they have short cuted .
Remember every year the flu virus changes so last years vaccine will not be as effective or might not work at all.
So in the space of a few weeks the vaccine companies come up with a new vaccine for the current flue and that vaccine some times will change several times in a single season.
The vaccine that the north should have finished taking will be different to the one we will get in the south in a few months time .