Fig. (3) Virus isolation from mouse lungs after sequential challenge with homologous and heterologous influenza viruses followed by SGB serotype II streptococcus infection. Groups of mice were immunized twice using 106 EID50 LAIV, GBSV or combined LAIV+GBSV; 3 weeks post-boost the mice were challenged with 500 MID50 of the A(H7N3)-wt influenza virus or with 100 MID50 of A/PR8/34 influenza virus and infected with 107 CFU of type II GBS 24 hours later. Infectious virus was isolated in CE from lung homogenates obtained on 48 and 96 hours post infection (h.p.i.) with challenge viruses, and expressed as a log10EID50/ml; (*) - p=0.029, (**) - p= 0.028.