The Pharmaceutical Journal
Vol 274 No 7345 p445
16 April 2005

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Combination vaccine shows reduced effectiveness

New data suggest that a combination pneumococcal-meningococcal vaccine may not be a suitable replacement for separate pneumococcal and meningococcal vaccines.

Jim Buttery, formerly of the University of Oxford, and colleagues conducted a randomised controlled trial involving 240 infants in the UK. The infants received either a combination 9-valent pneumococcal-group C meningococcal conjugate vaccine or monovalent group C meningococcal conjugate vaccine at ages two, three and four months along with routine immunisations (diphtheria, pertussis, tetanus, Haemophilus influenzae type b and oral polio).

The investigators measured group C meningococcal immunogenicity one month after the third dose of the vaccines. They found that immunogenicity was reduced in the combination versus the single vaccine (P<0.001), and the proportion of infants achieving the protective threshold titre was also lower in the combination vaccine group (P=0.05)

In addition, the average number of Hib antibodies produced was lower in the group that received the combination vaccine (P=0.02), although there was no difference in the proportion achieving the protective threshold. The number of antibodies against diphtheria was also lower in the combination group (P<0.001), although all infants in both groups achieved the protective threshold of antibodies.

The investigators note that the combination vaccine was immunogenic for all pneumococcal serotypes. They say that both vaccines were well-tolerated, although more infants in the combination group experienced irritability and decreased activity after the third dose.

The investigators comment: “The reduced immunogenicity of the serogroup C meningococcal component of Pnc9-MenC as well as concomitantly administered Hib and diphtheria may limit its further development.” They say that this is particularly relevant in the UK, where, in recent years, an increase in Hib vaccine failures has been observed as well as a potential lack of long-term protection following administration of meningococcal C vaccine in infants. “In this context, a combination vaccine offering lower initial group C meningococcal immunogenicity would be unlikely to be acceptable,” they say (JAMA 2005;293:1751).