How come germs come around fall winter an the flu shots are availible then? why are germs around now not in spring/summer? we're do germs come from?

Who knows: It is good that during warm weather it is very rare. Just imagine you have to deal with it all year round...

The virus multiplies: For viruses, like influenza, to make more copies of itself it has to use other animals' cells. It can then spread from animal to animal, and person to person. In the winter, many more people are inside, with the windows closed, and breathe on each other more and help spread the virus, which keeps on making more and more copies of itself. Getting more people together at holidays also adds up.