Each year over 650,000 children under age 5 die of pneumonia, an infection of the lungs – that’s more than HIV, tuberculosis and malaria combined.

Streptococcus pneumoniae – aka the pneumococcus bacteria– is amongst the leading causes of childhood pneumonia. It’s commonly carried in the nasopharynx (the back of the nose and throat) in healthy people, mostly children.

Pneumococcal disease occurs when the bacteria move from this harmless location to other more vulnerable parts of the body, including the lungs (pneumonia) or more invasive locations such as the blood (bacteremia and sepsis) or the membranes that surround and protect the brain (meningitis).
Vaccines targeting the outer carbohydrate capsule of Streptococcus pneumoniae have existed since the 1940s; however, these formulations of vaccine were not effective in children, who are most likely to carry the bacteria and therefore most vulnerable to infection and death by pneumococcal disease.

In the last two decades, new scientific technology has allowed for the creation of so-called "conjugate" vaccines against pneumococcus that work very well in children. These PCVs link part of the outer carbohydrate capsule of the pneumococcal bacteria to a protein, which makes it possible for children to mount a strong immune response that can protect against disease.

Because of the high cost of developing and manufacturing PCVs, they are some of the most expensive vaccine products on the market – for example, in the United States it costs over $720 for a child’s recommended four doses.

This extreme cost meant that PCVs were licensed and used almost exclusively in high-income countries for the first decade of their existence; lower-income countries simply could not afford to provide them for poor children. With the help of organizations like Gavi, the Vaccine Alliance, who began subsidizing the cost of PCV for low- and middle-income countries in 2009, the vaccine has now been introduced in nearly every country in the world.

Kenya is one of the pioneering countries who became an early adopter of PCV in 2011. However, before studies like PCVIS, not much was known about whether the vaccine works differently in developing countries than it does in developed countries like the United States, where initial vaccine trials were conducted.

PCVIS is one of the first studies to evaluate the impact of routine PCV use in a lower-middle-income country setting

PCVIS leverages the Kilifi Health and Demographic Surveillance System (KHDSS), an extremely robust demographic and health data collection system established in Kilifi in 2000. Because KHDSS has meticulously documented demographic information about births, deaths, migration, etc., it provides the ideal baseline and contextual data required to measure the impact of health interventions, especially vaccines such as PCV. Each resident has a unique identifier, and this enables the linking of demographic, hospital and laboratory data which provides a powerful means of understanding individual and population level patterns of health and disease.