The US FDA has approved four pandemic flu vaccines – from CSL, Medimmune, Novartis and Sanofi-Pasteur – for marketing in the US. The FDA has thus beaten Europe in the speed of its approval process, although they are not the first pandemic flu vaccines to be approved – China has already approved a pandemic flu vaccine from Sinovac Biotech.Initial lots of the 2009 H1N1 influenza virus vaccines are expected to become available in the next four weeks, the FDA says.Preliminary data show that the 2009 H1N1 vaccines induce a robust immune response in most healthy adults eight to 10 days after a single dose, the agency says ( scripnews.com, September 15th, 2009). Clinical studies are under way to provide additional information about the optimal dose in children.The most common side-effect is soreness at the injection site. Other side-effects include mild fever, body aches and fatigue for a few days after the inoculation. For the nasal spray vaccine, the most common side-effects include runny nose or nasal congestion in all ages, sore throats in adults and, in children two to six years of age, fever.