On September 15, 2009, four influenza vaccine manufacturers received approval from the Food and Drug Administration for use of influenza A (H1N1) 2009 monovalent influenza vaccines in the prevention of influenza caused by the 2009 pandemic influenza A (H1N1) virus. Both live, attenuated and inactivated influenza A (H1N1) 2009 monovalent vaccine formulations are available; each contains the strain A/California/7/2009(H1N1)pdm. None of the approved influenza A 2009 (H1N1) monovalent vaccines or seasonal influenza vaccines contains adjuvants. CDC's Advisory Committee on Immunization Practices has made recommendations previously for which persons should be the initial targets for immunization with influenza A (H1N1) 2009 monovalent vaccines and has issued guidelines on decisions for expansion of vaccination efforts to other population groups. Children aged 6 months--9 years receiving influenza A (H1N1) 2009 monovalent vaccines should receive 2 doses, with doses separated by approximately 4 weeks; persons aged >or=10 years should receive 1 dose.