Streptococcus pneumoniae is a bacterium that can cause severe infectious, such as pneumonia, bloodstream infection and meningitis. There are over 90 different types of pneumococcus and these different types can be differentiated by the outer carbohydrate capsule of the bacteria.
Vaccines against Streptococcus pneumoniae
Vaccines against the carbohydrate capsule of Streptococcus pneumoniae have existed since the 1940s; however, these formulations of vaccine were not effective in children. 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 conjugate vaccines 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.
Pneumococcal conjugate vaccines work in high income settings
The first pneumococcal conjugate vaccine (PCV) was developed against 7 types of pneumococcus and was named PCV7. Since then vaccines that offer protection against additional types of pneumococcus have been developed (PCV10 and PCV13). The introduction of PCV7 in the childhood immunisation programme in the USA led to a reduction in invasive pneumococcal disease (IPD), including pneumonia, in both children and adults. The indirect or "herd" protection seen in adults was because vaccinated children are less likely to carry vaccine-type pneumococci in the back of their noses and are therefore less likely to pass the bacteria to adults.
PCVIS is one of the few studies looking at the impact of PCV10 in low and middle income settings.
Why monitoring PCV impact is important
Although PCV7 led to significant reduction in invasive pneumococcal disease in the USA, in some populations its effect was greatly diminished. It was found that although the vaccine cleared the 7 serotypes of pneumococcal bacteria, their place was taken other serotypes, some of which caused IPD. This is known as serotype replacement disease. It is one of the reasons why the introduction of PCV immunisations should go hand in hand with good surveillance systems for early detection of potential serotype replacement disease.
Tackling the high cost of pneumococcal conjugate vaccines
Technology to develop and produce pneumococcal conjugate vaccines is expensive and to re-coup costs, manufacturers place a high price on the vaccines. Left to market forces, these vaccines would have taken many more decades to reach low income countries. Gavi, the Vaccine Alliance, bought PCV from the manufacturers for low income countries that had good vaccine coverage. Kenya was among the first countries to take up the offer.
Gavi only supports countries willing to incrementally take on the cost of the vaccine and, after a number of years, be fully responsible for the provision of these vaccines in their child immunisation programmes. For this to succeed, policy makers in participating countries need to know the impact of PCV and its cost effectiveness in order to justify health budget spend on this expensive vaccine. Kenya is due to being its transition from Gavi subsidy of PCV10 in 2021.