Effect of 10-valent pneumococcal conjugate vaccine on the incidence of radiologically-confirmed pneumonia and clinically-defined pneumonia in Kenyan children: an interrupted time-series analysis

Abstract

Summary Background 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. We examined the effect of 10-valent PCV on the incidence of pneumonia in Kenya. Methods We 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. We 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. Findings 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 (95% CI 0·32–0·86), 0·73 (0·54–0·97), and 0·63 (0·31–1·26), 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. Interpretation 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 re...

Estimating the impact of pneumococcal conjugate vaccines on childhood pneumonia in sub-Saharan Africa: A systematic review

“…Silaba et al also reported a 48% decline in radiological pneumonia in the entire under-five population. A similar trend was observed in the age groups with the 12 – 23 month group experiencing the greatest reduction in radiological pneumonia(47).…”

“…Individual studies showed variability in their definition of clinical, radiological and identification of pneumococcal pneumonia. Most studies applied the WHO standards for identification of Radiological pneumonia and clinical pneumonia (23,39,43). One study based pneumonia diagnosis on ICD-10 coding from clinical notes(44).…”

“…Four population based studies evaluated the impact of 10- or 13-valent vaccine on clinical pneumonia with inconsistent findings. Silaba et al reported a decline in hospitalization for severe or very severe pneumonia based on WHO clinical definition(47). Mackenzie et al showed no significant decline in clinical pneumonia incidence in all under-five age groups three years after 13-valent PCV introduction.…”

“…Two impact studies evaluated radiological pneumonia as an outcome(23,47). Mackenzie et al reported a decline in WHO defined radiological pneumonia in all age groups with decline in the range of 22 – 29%.…”

“…The WHO standardised definition of clinical and radiological pneumonia is markedly helpful in this situation as it ensures consistency irrespective of study location(55). Studies conducted in locations with a functional health and demographic surveillance system like in the Upper River region of The Gambia and in Kilifi, in Kenya(37,39) were particularly robust as they combined consistent pneumonia surveillance methods with up-to-date population information. Some studied relied on routine clinical data which is usually of variable quality(31,41).…”