Immunogenicity of combined vaccines in infants Helena Käyhty, PhD National Public Health Institute Dept of Vaccines Helsinki, Finland

Combined vs. reference administration hexavalent vaccines Gylca et al. Vaccine 2001: DTaP-HBV-IPV / Hib vs. DTwP-IPV mixed with Hib +HBV at 6, 10, 14 weeks Schmitt et al. J Ped 2000: mixed vs. separate DTaP- HBV-IPV / Hib at 2, 3, 4 months Mallet et al. PIDJ 2000: DTaP-HBV-IPV-Hib vs. DTaP- IPV-Hib / HBV at 2, 4 and 6 months

Combined vs. reference administration

Eskola et al. Lancet 1996 Vaccinations at 4 and 6 mo

Three doses, combined vs. separate administration in different studies

Mechanisms??? Missing adjuvant effect of wP Epitopic supression - antigenic competition Physicochemical interference

Immunogenicity trials in Sweden (3,5,12 mo) and Finland (4,6,14 mo)

T B B B B HELP Anti-CHO Ab Anti-Tetanus Ab CHO Tet

B HELP Anti-CHO Ab Anti-Tetanus Ab

PncT, PRP-T and T simultaneously Dose of PncT and response to PRP-T and Tetanus toxoid (Dagan et al. 1998)

Concomitant administration 2 cm apart in the same leg at 2, 4 and 6 mo Eskola et al.

Clinical implications? Are the induced anti-Hib responses high enough for protection? Experience from Finland, Sweden, the UK and Germany

Protective efficacy vs. antibody response

Immunogenicity trials in Sweden (3,5,12 mo) and Finland (4,6,14 mo)

Three doses, combined vs. separate administration in different studies

DTaP/Hib/(IPV) combinations in Germany Schmitt et al year follow up after the introduction of combined vaccines Overall VE97.5 % ( ) 1 dose88.6 % ( ) 2 doses95.1 % ( ) 3 doses98.8 % ( )

Measurement of the immune response to vaccination Vaccine  Sample  Antibody

Capsular polysaccharides (PS) Antibodies protective Poor and short lasting immune response in infants and children Long lasting antibody response in older children and adults TI-antigens -> no memory -> protection is based on existing antibodies

Conjugate vaccines???? immunogenicity improved by conjugating PS to carrier proteins -> TD properties -> antibody response even in infancy development of memory protection may last longer than detectable antibody memory B cells triggered upon challenge -> high and quick antibody response increase in avidity -> antibodies may function better

How to test development of memory Memory B cells Priming with conjugate and booster with PS – PS mimics contact with bacteria – more memory B cells to be triggered by PS – high antibody response of IgG isotype Avidity maturation

Increasing Affinity / Avidity

Geometric mean titer (GMT) and GM avidity index (GMAI) Goldblatt et al., JID 177, 1998, Avidity Index (GMAI) Anti-PRP Igg (GMT µg/ml) Age (months) Avidity Titre

Poolman et al Vaccine 2001

Avidity of anti-6B Pnc PS - primary seria at 2,4,6 mo with a conjugate - booster at 14 mo with conjugate or PS

Laboratory surrogates for evaluation of new conjugates, modified from Frasch 1995 antibody response in infancy persistence of antibodies (up to booster dose) induction of immunologic memory PS-vaccine avidity isotype/subclass distribution and avidity of antibodies functional activity of antibodies (opsonic or bactericidal activity )

Mucosal immune response is or may be important when local mucosal infection colonization precedes disease the role as a surrogate test unknown