by Micah Silaba, MMed; Michael Ooko, MSc; Christian Bottomley, PhD; Joyce Sande, MMed; Rachel Benamore, FRCR; Kate Park, FRCR; James Ignas, MD; Kathryn Maitland, FMedSci; Neema Mturi, MMed; Anne Makumi, MSc; Mark Otiende, MSc; Stanley Kagwanja, Dip MIS; Sylvester Safari, Dip MIS; Victor Ochola, BSc; Tahreni Bwanaali, MBA; Evasius Bauni, PhD; Fergus Gleeson, FRCR; Maria Deloria Knoll, PhD; Ifedayo Adetifa, PhD; Kevin Marsh, FMedSci; Thomas N Williams, FMedSci; Tatu Kamau, MPH; Shahnaaz Sharif, MD; Orin S Levine, PhD; Laura L Hammitt, MD; and J Anthony G Scott, FMedSci
To be published in The Lancet Global Health, March 2019. DOI:https://doi.org/10.1016/S2214-109X(18)30491-1
Pneumococcal conjugate vaccines (PCV) are highly protective against invasive pneumococcal disease caused by vaccine serotypes, but the burden of pneumococcal disease in low-income and middle-income countries is dominated by pneumonia, most of which is non-bacteraemic. Researchers examined the effect of 10-valent PCV on the incidence of pneumonia in Kenya. Researchers linked prospective hospital surveillance for clinically-defined WHO severe or very severe pneumonia at Kilifi County Hospital, Kenya, from 2002 to 2015, to population surveillance at Kilifi Health and Demographic Surveillance System, comprising 45,000 children younger than 5 years. Chest radiographs were read according to a WHO standard. A 10-valent pneumococcal non-typeable Haemophilus influenzae protein D conjugate vaccine (PCV10) was introduced in Kenya in January, 2011. In Kilifi, there was a three-dose catch-up campaign for infants (aged <1 year) and a two-dose catch-up campaign for children aged 1–4 years, between January and March, 2011. Researchers estimated the effect of PCV10 on the incidence of clinically-defined and radiologically-confirmed pneumonia through interrupted time-series analysis, accounting for seasonal and temporal trends. Between May 1, 2002 and March 31, 2015, 44,771 children aged 2–143 months were admitted to Kilifi County Hospital. We excluded 810 admissions between January and March, 2011, and 182 admissions during nurses' strikes. In 2002–03, the incidence of admission with clinically-defined pneumonia was 2170 per 100,000 in children aged 2–59 months. By the end of the catch-up campaign in 2011, 4997 (61·1%) of 8181 children aged 2–11 months had received at least two doses of PCV10 and 23 298 (62·3%) of 37,416 children aged 12–59 months had received at least one dose. Across the 13 years of surveillance, the incidence of clinically-defined pneumonia declined by 0·5% per month, independent of vaccine introduction. There was no secular trend in the incidence of radiologically-confirmed pneumonia over 8 years of study. After adjustment for secular trend and season, incidence rate ratios for admission with radiologically-confirmed pneumonia, clinically-defined pneumonia, and diarrhoea (control condition), associated temporally with PCV10 introduction and the catch-up campaign, were 0·52, 0·73, and 0·63, respectively. Immediately before PCV10 was introduced, the annual incidence of clinically-defined pneumonia was 1220 per 100,000; this value was reduced by 329 per 100 000 at the point of PCV10 introduction. Over 13 years, admissions to Kilifi County Hospital for clinically-defined pneumonia decreased sharply (by 27%) in association with the introduction of PCV10, as did the incidence of radiologically-confirmed pneumonia (by 48%). The burden of hospital admissions for childhood pneumonia in Kilifi, Kenya, has been reduced substantially by the introduction of PCV10. This study is funded by the Gavi, The Vaccine Alliance and Wellcome Trust. Access the full article here. Also be sure to read the accompanying editorial by Corinne Levy and Robert Cohen, Tackling childhood pneumonia in Africa: a dream that becomes reality:
"The close relationship between pneumococcus and pneumonia is a very old story. In 1882, Friedlander reported pneumococci in tissue from humans with pneumonia and, in 1884, recovered pneumococci from the blood of patients with pneumonia for the first time. However, regardless of the microbiological method used (culture, antigen detection, or molecular tools), only a small proportion of pneumonia cases can be attributed to pneumococcus, and pneumococcal bacteraemic pneumonia represents only a small portion of pneumonia cases. There is a disparity between the low proportion of pneumonia cases attributed to pneumococcus (7·2%), even if more accurate diagnostic methods are used, and the large worldwide reported effect of pneumococcal conjugate vaccines (PCVs) on pneumonia. This contrast highlights the need to specifically assess the effect of PCV implementation on pneumonia, particularly in low-income countries.