Intranasal immunization of mice with a mixture of the pneumococcal proteins PsaA and PspA is highly protective against nasopharyngeal carriage of Streptococcus pneumoniae

Acquisition of pneumococci is generally from carriers rather than from infe cted individuals. Therefore, to induce herd immunity against Streptococcus pneumoniae it will be necessary to elicit protection against carriage. Caps ular polysaccharide-protein conjugates, PspA, and PsaA are known to elicit some protection against nasopharyngeal carriage of pneumococci but do not a lways completely eliminate carriage. In this study, we observed that PsaA e licited better protection than did PspA against carriage. Pneumolysin elici ted no protection against carriage. Immunization with a mixture of PsaA and PspA elicited the best protection against carriage. These results indicate that PspA and PsaA may be useful for the elicitation of herd immunity in h umans. As PspA and pneumolysin are known to elicit immunity to bacteremia a nd pneumonia, their inclusion in a mucosal vaccine may enable such a vaccin e to prevent invasive disease as well as carriage.