Abstract 976 Poster Session IV, Tuesday, 5/4 (poster 178)

Background: In our previous randomized controlled trial in toddlers 15 to 23 months of age, priming with 2 doses of MenC (Chiron)2 months apart elicited a robust response to a dose of MenPS 1 year later. Priming with 2 doses of MenPS resulted in a hyporesponsive state to MenPS boost 1 year later compared to control toddlers who had received 2 doses of hepatitis B vaccine prior to receiving a dose of MenPS 1 year later (JAMA 1998; 280:1685-9).

Objectives: To observe the safety and immunogenicity of a single dose of MenC in these healthy now 41-55 mo olds who had previously received 1 (HB vaccine group) or 3 (MenPS)doses of MenPS but no prior MenC doses.

Methods: Open label extension for all toddlers who had received either 3 doses MenPS (study time 0, 2 mo 14 mo) or 2 doses HB vaccine (study time 0, 2 mo) followed by 1 dose MenPS (study time 14 mo). After informed consent, 1 dose MenC IM was administered (study time 29-35 mo). Serum collected pre (study time 29-35 mo) and 1 month post (study time 30-36 mo) for total IgG anticapsular group C antibody response (ELISA) and bactericidal Ab response to N. meningiditis group C. Adverse reactions were recorded by parents for 7d, and also reviewed at 30d.

Results: 98 of 129 eligible subjects enrolled; 51 of 67 of MenPS group, 47 of 62 of HB group. Men C was well tolerated and no severe reactions were reported.

Response to MenC as Measured by Anticapsular Antibody Response (ELISA) u/ml and Bactericidal Antibody Response (Table)

Table 1 No caption
Full size table

Conclusions: MenC is safe and immunogenic in young children who have previously received 1 or 3 doses of MenPS as toddlers. Multiple previous doses of MenPS led to a less robust response to MenC even if last MenPS dose was more than 1 year previously.

Implications: Multiple doses of MenPS should be avoided if possible. MenC can partially overcome multi-dose MenPS hyporesponsiveness.