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Volume 30, Number 11—November 2024
Research

Estimating Influenza Illnesses Averted by Year-Round and Seasonal Campaign Vaccination for Young Children, Kenya

Radhika Gharpure, Young M. Yoo, Ben Andagalu, Stefano Tempia, Sergio Loayza, Chiedza Machingaidze, Bryan O. Nyawanda, Jeanette Dawa, Eric Osoro, Rose Jalang’o, Kathryn E. Lafond, Melissa A. Rolfes, and Gideon O. EmukuleComments to Author 
Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA (R. Gharpure, Y.M. Yoo, B. Andagalu, K.E. Lafond, M.A. Rolfes, G.O. Emukule); Centers for Disease Control and Prevention, Nairobi, Kenya (B. Andagalu, G.O. Emukule); World Health Organization, Geneva, Switzerland (S. Tempia, C. Machingaidze, M.A. Rolfes); Pan American Health Organization, Washington, DC, USA (S. Loayza); Kenya Medical Research Institute, Kisumu, Kenya (B.O. Nyawanda); Washington State University Global Health Kenya, Nairobi (J. Dawa, E. Osoro); Washington State University, Pullman, Washington, USA (E. Osoro); Ministry of Health, Nairobi (R. Jalang’o)

Main Article

Table 1

Model input variables and data sources in study to estimate influenza illnesses averted by year-round and seasonal campaign vaccination for young children, Kenya*

Model input Value Data source
Population characteristics
Population size, children 6–23 mo of age 1,809,394 2022 census projection using 2019 census (15) and World Bank annual population growth rates (16)
Annual vaccination coverage, %
 60
 Assumption based on coverage calculated in first year of pediatric demonstration project; both strategies obtained similar coverage (6)
Influenza illnesses
Influenza-associated hospitalization rate 146.6/100,000 population Rate among children <2 y of age during 2011–2014 (17)
Ratio of nonhospitalized to hospitalized
influenza illnesses		 19.9 (IQR 17.6–21.6) Calculated from Siaya County SARI surveillance data and healthcare utilization survey (Appendix Figure 3)
Influenza illnesses medically attended, %
 47.9
 Healthcare utilization survey: results for children <2 y of age in Kenya (18)
Vaccine effectiveness and natural immunity
VE point estimate, % 50 (average) 2010–2012 clinical trial data for trivalent influenza vaccine in children <5 y of age in Kenya (19) and meta-analysis of influenza VE among children 6–23 mo of age (20)
Rate of waning (base scenario) VEt = 70 – 1.37 × biweeks + 0.18 × biweeks2 – 0.03 × biweeks3 †
(≈7% absolute decline per month)		 Prior analyses evaluating influenza vaccination timing among older adults (11)
Duration of natural immunity from infection 12 mo Assumption consistent with prior models that did not assume reinfections within a 12-mo time horizon (8,10)

*VE, vaccine effectiveness. †VEt refers to vaccine effectiveness at time t, calculated based on the number of biweeks (period of 2 weeks) elapsed.

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Page created: October 07, 2024
Page updated: October 22, 2024
Page reviewed: October 22, 2024
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