Serum Cross-Reactive Antibody Response to a Novel Influenza A (H1N1) Virus After Vaccination with Seasonal Influenza Vaccine

May 22, 2009 As of May 2009, a total of 5,469 confirmed cases of human infection with a novel influenza A (H1N1) virus was documented in 47 states and the District of Columbia. In addition, the virus spread to 41 countries, with a total of 4,774 cases reported in countries outside the United States. Because producing a novel influenza A (H1N1) virus vaccine can take several months, determining whether the seasonal influenza vaccine offers any protection against the novel influenza A (H1N1) virus is important. Using stored serum specimens collected during previous vaccine studies, CDC assessed the level . . .