HAI titers against 2009 H1N1 isolates.

HAI titers against different strains of new H1N1 viruses were determined using immune sera collected from mice at week 5 after immunization with A/California/04/2009 VLP vaccine (immune sera), from mice infected with A/California/04/2009 (infected sera), or naïve sera. 1Wild type A/California/04/2009 virus. 2Three reassortant viruses, kindly provided by Dr. Ruben Donis (CDC, Atlanta, GA), were generated with six A/PR/8/34 internal genes and with HA and NA of A/Texas/5/2009, A/Texas/5/2009* (Q226R mutation in HA), A/New York/18/2009 respectively. Viruses were grown in eggs and used for HAI titers using 4 HA units.