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Survival of influenza-infected mice after secondary challenge with Streptococcus pneumoniae. Groups of 6 to 7 mice were infected with 1000 TCID50 of influenza virus and then challenged 7 d later with either PBS (closed squares) or 1 × 105 CFU of pneumococcus D39 (serotype 2, open circles), A66.1 (serotype 3, closed triangles), or T4 (serotype 4, open triangles). *, P < 0.05 (Mantel-Cox χ2) versus other groups.
