A vaccine aimed at preventing both pneumococcal disease and meningitis elicits a lower immune response against the meningitis bug than does the single component vaccine, results of a clinical trial show.

Dr. Jim P. Buttery and colleagues report their findings in this week’s Journal of the American Medical Association.

Buttery, at the University of Melbourne in Parkville, Australia, and his team compared a group C meningococcal vaccine (MenC) against a candidate combination pneumococcal-and-meningococcal vaccine dubbed Pnc9-MenC.

In each group, 120 infants were given three doses of vaccine at ages 2, 3, and 4 months along with routine childhood inoculations.

When the infants were tested at age 5 months, levels of antibodies against the meningitis organism were four times greater in the MenC group than the Pcn9-MenC group. The proportion of infants in each group with adequate antibody levels was 94 percent versus 81 percent, respectively.

This study “illustrates the unpredictability of immunogenicity when combining multivalent vaccines,” Buttery’s group points out.

The Pcn9-MenC vaccine tested “may not be a suitable replacement” for individual MenC or pneumococcal vaccines, they conclude.

SOURCE: Journal of the American Medical Association, April 13, 2005.