Pneumococcal vaccination of children in Kenya can provide ‘herd protection’ to unvaccinated population

Findings suggest vaccine will be effective in other low-income countries

The introduction of a new pneumococcal vaccine in routine immunisation programmes in Kenya reduced levels of the pneumococcal bacterium in two-thirds of the population, both among vaccinated and unvaccinated individuals. This level of coverage is expected to provide herd protection against pneumococcal disease to the whole population, according to a new study published in The Lancet Global Health.

Pneumococcal infections can lead to pneumonia, meningitis, or septicaemia, and are the leading cause of vaccine-preventable deaths among children under five years of age worldwide.

Researchers from Kenya, the UK and US, working in partnership with the London School of Hygiene & Tropical Medicine, looked at the effectiveness of the introduction of pneumococcal conjugate vaccine PCV10 in Kenya, which protects against 10 serotypes (strains) of the bacteria. Kenya was among the first African countries to introduce PCV in 2011, and the first low-income country to use the 10-valent vaccine. The 10 serotypes included in the vaccine account for at least 70% of pneumococcal disease in every region of the world and have the potential to greatly reduce pneumococcal disease.

A large proportion of the population “carries” the bacteria in the back of the nose without any symptoms. By vaccinating certain individuals and reducing their carriage of the bacterium, the rest of the population can be given ‘herd protection’ by reducing transmission of the bacterium to unvaccinated individuals. This is the first time PCV10 has been shown to be effective in a low-income country.

Researchers at the KEMRI-Wellcome Trust Research Programme conducted the study in Kilifi, Kenya, where infants under 12 months old received the three-doses of PCV10 and children aged one to five received up to two doses as part of a catch-up campaign.

Using data collected two years before and two years after PCV10 was introduced, researchers compared carriage of pneumococcal bacterium in children under 5 years (the vaccinated age group) and unvaccinated persons 5 years and older.

Senior author Anthony Scott, Professor of Vaccine Epidemiology and Director of the Vaccine Centre at the London School of Hygiene & Tropical Medicine, said: “Our study shows that after the introduction of PCV10 in Kilifi, carriage of vaccine serotypes was reduced by two-thirds both in children younger than 5 years and in older individuals. These findings suggest that PCV10 introduction in Africa will have substantial indirect effects on invasive pneumococcal disease.”

The research was conducted by KEMRI-Wellcome Trust Research Programme, Johns Hopkins Bloomberg School of Public Health, University of Oxford, Kenya Ministry of Health and the London School of Hygiene & Tropical Medicine. It was funded by the GAVI Alliance and Wellcome Trust.

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Full Paper
Laura L Hammitt, Donald O Akech, Susan C Morpeth, Angela Karani, Norbert Kihuha, Sammy Nyongesa, Tahreni Bwanaali, Edward Mumbo, Tatu Kamau, Shahnaaz K Sharif, Anthony G Scott. Population effect of 10-valent pneumococcal conjugate vaccine on nasopharyngeal carriage of Streptococcus pneumoniae and non-typeable Haemophilus influenzae in Kilifi, Kenya: findings from cross-sectional carriage studies. The Lancet Global Health. DOI: 10.1016/S2214-109X(14)70224-4.

Photo: Child receives vaccine, Credit: GAVI_2013_Evelyn-Hockstein-_KENYA