By tracking the incidence of pneumococcal disease (pneumonia, meningitis and sepsis) before and then after PCV was introduced, our study can determine how much disease has been prevented by the use of the vaccine.
The Gavi-supported PCV10 program reduced hospital admissions for pneumonia in children under five by more than one quarter after four years of vaccine use.
An important component of pneumococcal disease transmission is the carriage of the bacteria in the nose of healthy children and adults - potential pneumococcal disease is commonly spread by asymptomatic carriers within communities. Because carriage of the bacteria is a necessary first step for a person to become sick with pneumococcal disease and/or spread the bacteria to others, reducing carriage is likely to reduce transmission of the bacteria and therefore the number of cases of disease. Our study is measuring community carriage of pneumococcus in Kilifi along with pneumonia and invasive pneumococcal disease to gain a more comprehensive understanding of vaccine impact, beyond the impact on disease alone.
The Gavi-supported PCV10 program reduced the carriage of vaccine-type bacteria in Kenya, but not to the very low levels seen in middle- and high-income countries.
Although pneumococcal disease is a major cause of disease and death in children, it also affects the rest of the population, especially elderly adults and those who are immunocompromised. Because PCV works largely by reducing transmission via carriage in healthy people, it has the potential to protect even those who haven’t been vaccinated through herd protection. In addition to measuring vaccine impact in vaccinated children, we also looked at the potential impact on disease and transmission in unvaccinated people.
The Gavi supported PCV10 program reduced vaccine-type IPD in unvaccinated populations (those under two months, or too young to be vaccinated, and those over five years or too old to be vaccinated), showing that PCV10 provided substantial population protection/herd immunity.
Early use of PCVs in developed country settings have shown evidence that strains not included in the vaccines could begin replacing vaccine-type strains in terms of the amount if transmission and disease they cause. If the magnitude of replacement is high enough, it has the potential to significantly reduce the overall impact of vaccine use. As part of our analysis, we sought to identify and quantify this potential serotype replacement.
Because PCVIS is embedded in a robust demographic health system, which includes the Kilifi Vaccine Monitoring Study (KiVMS), we are able to track the number of children who are vaccinated each year, including detailed information about the number of vaccine doses each child receives and the timeliness of each. This allows an in-depth understanding of vaccine coverage in the population, which can offer insights about the functionality of the health system as well as context for interpreting the measured vaccine impact on disease and transmission.
Because the cost of introducing PCV is substantially subsidized for Gavi-eligible countries, the decision to begin and continue a Gavi-supported PCV program is often an obvious choice. However, as countries like Kenya approach Gavi graduation and the subsequent requirement to fully self-finance their vaccine programs, the exact calculation of the costs and benefits of expensive products such as PCV becomes more complicated. We performed a cost-effectiveness evaluation of the PCV program to inform evidence-based decisions about its continuation without Gavi support, which is projected to end in 2027.
Poster, 11th International Symposium on Pneumococci and Pneumococcal Diseases, 15-19 April 2018, Melbourne, Australia.
KEMRI-Wellcome Trust Research Programme Centre for Geographic Medical Research Coast (CGMRC) Hospital Road, Next to Kilifi County Hospital P.O. Box 230-80108 Kilifi, Kenya Email: firstname.lastname@example.org