Hi, Though the most common side effects of H1N1 vaccine could be muscle aches, fever, runny nose, wheezing and headache, possibility of any serious diseases like Guillain-Barré syndrome that causes muscle weakness and paralysis is quite rare. Earlier some cases of GBS have been reported with vaccine but they were in very rare instances. If you suffer continuous muscle weakness or notice any paralysis of leg muscles, please arrange an appointment with a neurologist right away who will evaluate the possibilities here and can provide you an appropriate treatment. Hope this information proves helpful to you.Take Care & Regards!!!