Assessing the effect of social contact structure on the impact of pneumococcal conjugate vaccines

Abstract

AbstractAlthough pneumococcal conjugate vaccines (PCVs) have greatly reduced the incidence of invasive diseases caused by vaccine-targeted serotypes (VT) ofStreptococcus pneumoniae, vaccine impact may be eroded by the increase in rates of disease caused by non-vaccine serotypes (NVT) – a phenomenon known as serotype replacement. Here, we investigated the effect of social contact patterns on the dynamics of vaccine impact and serotype replacement in carriage.We developed a neutral, age-structured, susceptible–colonized (S–C) model incorporating VT-NVT co-colonization and childhood immunization with PCVs and verified it against real-world carriage data. Using empirically derived contact matrices from 34 countries, we assessed the impact of contact patterns of different age groups on the time-to-elimination, here defined as the time taken for the proportion of VT among circulating serotypes to drop to 5% of the pre-PCV level. Finally, we quantified the contribution of various parameters—such as vaccine efficacy, coverage, immunity waning, and population susceptibility—to the dynamics of VT elimination.Our model recapitulated the observed prevalence of carriage of VTs observed in the real-world data and showed that varying the contact structure alone led to different time-to-elimination (range: 3.8 – 6 years). We found that higher total contact rate and assortativity in children under 5 were key factors in accelerating VT elimination. In addition, higher vaccine efficacy and coverage, and slower immunity waning led to shorter time-to-elimination.These findings illuminate the mechanisms controlling the dynamics of vaccine impact and serotype replacement and may help predict the impact of the higher-valency PCVs in communities with different contact patterns.