What is it about?
Streptococcus pneumoniae is a bacterium responsible for over 300,000 child deaths globally each year. Various vaccines exist to prevent pneumococcal disease, each covering different types of the bacteria. While the introduction of new pneumococcal conjugate vaccines has reduced cases of diseases caused by the covered types, it has also led to an increase in non-vaccine types, a phenomenon known as serotype replacement. We developed a model that simulates the spread of the bacteria across different age groups, accounting for the coexistence and competition among various types in the presence of type- and age-specific vaccines. This model was calibrated using historical data on invasive pneumococcal disease in the U.S., focusing on specific age groups and bacterial types. Projections were made to compare the new vaccines against the current vaccination practices.
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Why is it important?
The model was used to compare the potential impact of a new vaccine, PCV15, in the US which protects against 15 types of the bacteria, to the PCV13 vaccine, which covers 13 types and was implemented in children vaccination program since 2010. The findings suggest that using PCV15 could lead to a 6.04% reduction in the incidence of IPD over the next 10 years compared to continuing with PCV13.
Perspectives
Dynamic transmission models are powerful tools for estimating how population-level susceptibility changes over time and how various factors, such as vaccination status and patterns of bacteria transmission, influence the spread of diseases. These models are particularly useful for understanding the indirect protection that vaccination can provide, not just to those vaccinated but also to the wider community. Our model allows for a detailed analysis of the indirect protection that pediatric vaccination provides to adults. This phenomenon, known as herd immunity, has been observed in various vaccination programs where pneumococcal vaccines are administered to children. By maintaining identical vaccination strategies for adults while comparing the two infant vaccination programs—PCV13 versus PCV15—we found that implementing PCV15 in the pediatric population could lead to additional reductions in adult disease, particularly for serotypes 22F and 33F. The flexibility and accuracy of our model suggest it could be adapted for use in different countries, taking into account local variations in pneumococcal epidemiology, such as differences in age distribution, vaccination history, dosing schedules, vaccine effectiveness, and specific serotypes of interest. While the focus of this manuscript has been on epidemiological outcomes, applications of the model could also evaluate the cost-effectiveness of various vaccines and vaccination strategies, further enhancing its utility in public health decision-making.
Tufail Malik
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This page is a summary of: A dynamic transmission model for assessing the impact of pneumococcal vaccination in the United States, PLOS One, April 2025, PLOS,
DOI: 10.1371/journal.pone.0305892.
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