This link to the Visa Wizard is a guide to help foreign citizens understand which visa category might be appropriate for their travel to the United States. http://travel.state.gov/content/visas/english/general/visa-wizard.html
For Attendees from Non-Participating Visa Waiver Program Countries:
To apply for a visa, visit http://travel.state.gov/content/visas/english.html
Visas should be applied for as early as possible and well in advance of the meeting. According to the National Academy of Sciences International Visitors Office, there has been a recent increase in scientists experiencing visa delays of greater than 3 months. Information about visa wait times can be found at http://travel.state.gov/content/visas/english.html
Be advised that you need to apply for Business Visitor Visa (B-1). IMMUNOLOGY 2016™ is a scientific meeting. You will be asked to name the meeting (“IMMUNOLOGY 2016™”) and explain the purpose of your visit.
NOTE: Registration refunds will not be issued after April 11, 2016, for any reason, including the inability to obtain a visa.
For Attendees from Participating Visa Waiver Program Countries:
Effective January 20, 2010, the Department of Homeland Security is transitioning to enforced compliance of the Electronic System for Travel Authorization (ESTA) requirement for Visa Waiver Program (VWP) travelers. Therefore, VWP travelers who have not obtained approval through ESTA should expect to be denied boarding on any air carrier bound for the United States.