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Determination of protection against a lethal intranasal pneumococcal challenge. Two weeks after the third immunization, mice were intranasally challenged with a 90% lethal dose of S. pneumoniae ATCC BAA-334 (A) or ATCC6308 (B). Survival rates were monitored for 14 days (n = 10/group). *, P < 0.05; **, P < 0.01; ***, P < 0.001; log-rank test. ns, not significant.
