LAUSR

Background Pertussis is a highly infectious disease and an important public health concern. The main aim of pertussis vaccination is to reduce the risk of severe pertussis in infants and young children, due to the high disease-related morbidity and mortality in this age group. While the introduction of whole-cell vaccine in the 1940s led to a dramatic decrease in cases and associated fatalities, its higher reactogenicity led to its replacement with acellular vaccines, which contain fewer antigens.(1) In Ireland, despite vaccination coverage rates of 95% from 2011–2018 average rates from 2014–2018 were more than double those from 2003–2008.(2) Infants under 6 months and adults between 35 and 44 years have been disproportionately affected.(3) Aim The aim of this review was to assess the effectiveness of wholecellular versus acellular pertussis; to analyse the relevance of recent trends in circulating strains including genetic divergent isolates; to assess the effectiveness of varying the number of antigen components in acellular vaccines and to determine the impact of different vaccination schedules on vaccine efficacy. Methods A review of the literature was performed across three electronic databases from January 1990 to October 2018, using key search terms. A search of grey literature using the same terms and time period was also conducted. Conclusion National Vaccination programs have not led to optimal pertussis control. Variations in scheduling or type of vaccine (wholecell or acellular) has not resulted in improved control. The change to acellular vaccination highlighted the relatively short-lived benefit on adaptive immunity and protection and lead to the introduction of booster vaccination doses at a younger age and at adolescence to counter waning immunity. Acellular vaccinations contain between one and five antigenic components. Vaccines which contain between three and five antigens demonstrate higher efficacy than vaccines with lower antigen components. In Denmark and Sweden effectiveness studies have shown some benefit in mono-component and two-antigen vaccines, although factors such as surveillance, diagnosis, variation in case definition and differences in uptake rates make comparison difficult. Mismatches between circulating strains and specific vaccine antigens, particularly pertactin, have been reported, although no evidence of higher virulence has been associated with these isolates. Whilst several variations in scheduling exist no superiority was demonstrated with any one approach. The results of this review do not indicate the benefit of a change in the scheduling or vaccine component of pertussis vaccines currently used in the Irish childhood vaccination programme.