Efficacy & Adverse Effects of Swine Flu Vaccine According to Interim Flu Vaccine Report by CDC, flu vaccine holds 45& efficacy. More specifically, it has 37% and 50% efficacy against Influenza A (H1N1) and Influenza B virus respectively. As far as the adverse effects of Swine Flu vaccine are concerned, there are some mild side effects which are common in case of every vaccine. They include • Sore arm at the site of injection • Redness at site of injection • Swelling at site of injection • Fatigue • Headache • Fever Specific adverse effects limited to Swine Flu vaccine are not adequately reported. Some cases of narcolepsy and Guillain-Barre syndrome were reported.