Makumi, A. | bioRxiv Science

bioRxiv2018

Coverage and timeliness of vaccination and the validity of routine estimates: Insights from a Vaccine Registry in Kenya

The benefits of childhood vaccines are critically dependent on vaccination coverage. We used a vaccine registry (as gold standard) in Kenya to quantify errors in routine coverage methods (surveys and administrative reports), to estimate the magnitude of survivor bias, contrast coverage with timeliness and use both measures to estimate population immunity.\n\nWe found coverage surveys in the 2nd year of life overestimate coverage by 2%. Compared to mean coverage in infants, static coverage at 12 months was exaggerated by 7-8% for third doses of oral polio, pentavalent (Penta3) and pneumococcal conjugate vaccines, and by 24% for the measles vaccine. Surveys and administrative coverage also underestimated the proportion of the fully immunised child by 10-14%. For BCG, Penta3 and measles, timeliness was 23-44% higher in children born in a health facility but 20-37% lower in those who first attended during vaccine stock outs.\n\nCoverage surveys in 12-23 month old children overestimate protection by ignoring timeliness, and survivor and recall biases.

epidemiology↗

bioRxiv2018

The impact of 10-valent Pneumococcal Conjugate Vaccine on the incidence of radiologically-confirmed pneumonia and clinically-defined pneumonia in Kenyan children.

BackgroundPneumococcal conjugate vaccines (PCV) are highly protective against invasive pneumococcal disease caused by vaccine serotypes but the burden of pneumococcal disease in developing countries is dominated by pneumonia, most of which is non-bacteraemic. We examined the impact of PCV on pneumonia incidence.\n\nMethodsWe linked prospective hospital surveillance for clinically-defined WHO severe or very-severe pneumonia at Kilifi County Hospital from 2002-2015 to population surveillance at Kilifi Health and Demographic Surveillance System, comprising 45,000 children aged <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 catch-up campaign for children aged <5 years. We estimated the impact of PCV10 on pneumonia incidence through interrupted time series analysis accounting for seasonal and temporal trends.\n\nFindingsThe incidence of admission with clinically-defined pneumonia in 2002/3 was 21{middle dot}7/1000/year in children aged 2-59 months. This declined progressively over 13 years. By the end of March 2011, 61{middle dot}1% of children aged 2-11 months received [≥]2 doses and 62{middle dot}3% of children aged 12-59 months received [≥]1 dose of PCV10. Adjusted incidence rate ratios for admissions with radiologically-confirmed pneumonia, clinically-defined pneumonia, and diarrhoea (control condition), associated with PCV10 introduction, were 0{middle dot}52 (95% CI 0{middle dot}32-0{middle dot}86), 0{middle dot}73 (95% CI 0{middle dot}54-0{middle dot}97) and 0{middle dot}63, (95% CI 0{middle dot}31-1{middle dot}26), respectively. The annual incidence of clinically-defined pneumonia in December 2010 was 12{middle dot}2/1000; this was reduced by 3{middle dot}3/1000 with PCV10 introduction.\n\nInterpretationOver 13 years, hospitalisations for clinically-defined pneumonia declined progressively at Kilifi County Hospital but fell abruptly by 27% in association with PCV10 introduction. The incidence of radiologically-confirmed pneumonia fell by 48%. The burden of childhood pneumonia in Kilifi, Kenya, has been reduced substantially by PCV10.\n\nFundingGavi, Wellcome Trust

epidemiology↗