THERAPY

Serogroup B meningococcal OMP vaccines: limited effectiveness

The effectiveness of any particular serogroup B meningococcal vaccine depends on whether the vaccine fits the epidemic strain, report researchers from a multinational study group. 1

This study involved infants aged < 1 year (n = 187), children aged 2-4 years (183) and adults aged 17-30 years (173). Each age group was randomised to receive 3 1M doses of 1 of 2 outer-membrane protein (OMP) meningococcal vaccines, based on different serogroup B epidemic strains (a Cuban Neisseria meningitidis strain or a Norwegian-based N. meningitidis strain), or a control vaccine, every 2 months. Infant and child controls received 3 doses of a Haemophilus injluenzae type b (Hib) polyribosylribitol phosphate tetanus conjugate vaccine; adult controls received a 3-dose series of aluminium hydroxide adjuvant dissolved in solvent.

Serum bactericidal activity (SBA) against homolog­ous vaccine type strains and a heterologous Chilean epidemic strain of N. meningitidis was used to assess vaccine efficacy. In addition, in order to identify possible immunodominant antigens responsible for homologous SBA, SBA assays were conducted on samples of infant serum from recipients of the Norwegian-based vaccine using 7 isogenic strains. * Vaccine response

Among infants, no significant between-group differences were observed in SBA response to the heterologous Chilean epidemic target strain. ** However, among both children and adults, recipients of either meningococcal vaccine were significantly more likely than control vaccine recipients to respond. A significant difference in response between the Norwegian- and Cuban-based vaccines was only seen in adults.

For all 3 age groups, recipients of the Cuban- and Norwegian-based vaccines were significantly more likely than controls to show SBA response against their respective homologous vaccine type strains.

For all 3 age groups, Cuban-based vaccine recipients were significantly more likely than Norwegian-based vaccine recipients to respond against the Cuban-based vaccine type strain. Similarly, for all 3 age groups, Norwegian-based vaccine recipients were significantly more likely than Cuban-based vaccine recipients to respond against the Norwegian-based vaccine type strain.

Mter 3 doses of vaccine, 98% of 53 serum samples from infants vaccinated with the Norwegian-based vaccine demonstrated a ~ 4-fold rise in antibody titre against the homologous Norwegian-based vaccine type strain devoid of class 3 OMP. In contrast, none of these serum samples demonstrated an SBA response against the Norwegian-based vaccine type strain devoid of class 1 OMP, except for 1 sample that had low titre against several heterologous strains.

1173-832419911186-000171$01.00° Adl.lntematlonal Limited 1999. All right. reaerved

New strategies for epidemics In an accompanying editorial, Dr Jay Wenger from

the WHO, Geneva, Switzerland, comments that the results of the above-mentioned study suggest that 'vaccines should be prepared to fit different epidemic strains as they occur' , for maximal benefit.2 However, Dr Wenger concedes that this approach 'requires coordination and commitment on the part of public health personnel, government, and industry to be fully successful.' Nevertheless, adds Dr Wenger, 'it is the best hope until vaccines that are effective against all serogroup B strains are developed' .

* The 7 isogenic strains included a class 1 OMP-dejicient strain (B:15:-); a class 3 OMP-dejicient strain (B:-:Pl.7,16); and strains B:15:P1.5.2; B:15:Pl.19,15; B:15:P1.7 b,4; B:15:Pl.J2,13; and B:15:P1.5 ·,10.

**lbccine response was defined as a ~ 4-fold rise from baseline in SBA antibody titre.

1. Tappcro IW, et al. Immunogcnicity of 2 serogroup B outer membrane protein meningococcal vaccines: a randomized controlled trial in Oillc. Journal of the

American McdicaI Association 281: IS20-IS27.28 Ape 1999 2. Wenger JD. Scrogroup B meningococcal disease: DeW outbreaks, DeW strategies. Journal of the American Mc:dk:aI Association 281: 1S41-1S43. 28 Apr 1999 ...,..,.,..

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