Does whole-cell pertussis vaccine protect black South African infants? Assessment of post-vaccination events and antibody responses to pertussis toxin, filamentous haemagglutinin and agglutinogens 2 and 3
The whole-cell pertussis vaccine currently used in South Africa has not been adequately evaluated for post-vaccination events and immunogenicity. A trial of this vaccine combined with diphtheria and tetanus toxoids (DTP) was undertaken in 115 black babies who received primary vaccination at 2, 4 and 6 months of age. Serological IgG responses to the major antigens of Bordetella pertussis, filamentous haemagglutinin (FHA), pertussis toxin (PT) and fimbriae (agglutinogens 2 and 3 (AGG 2 + 3), were evaluated by enzyme-linked immunosorbent assay in sera obtained at birth, and before vaccination at 2,4 and 6 months and at 9 months. Surprisingly, after 3 doses of DTP, responses to PT and FHA were found merely to restore levels of IgG to PT and FHA to those found in cord blood. In contrast with the positive increases in these antibodies found in other series of whole-cell vaccination, the anti-PT seroconversion rate was only 19% and the anti-FHA rate only 24%. High levels of anti-AGG 2 + 3 were produced with 67,2% seroconversion.
The frequency and nature of post-vaccination events were recorded. Incidences of all reactions to the vaccine were low (7,6%): Fever (3,2%) and excessive crying (2,4%) were the most frequency occurring minor events. The rate of neurological post-vaccination events (without sequelae) during the brief follow-up period was 2 hypotonic-hyporesponsive episodes (8,03/1 000 doses) and 1 convulsion (4,02/1000 doses).
Significant pertussis antibody levels were found in maternal and cord sera with levels in the latter frequently being higher. Three cases of pertussis occurred during the study period. Only 1 of the subjects had completed primary vaccination. In view of these findings, the need for a proper efficacy and safety study of the currently used DTP vaccine is urgently indicated in South Africa.