Seasonal influenza vaccination in Kenya: an economic evaluation using dynamic transmission modelling

Abstract

Background: There is substantial burden of seasonal influenza in Kenya, which led the government to consider introducing a national influenza vaccination programme. Given the cost implications of a nationwide programme, local economic evaluation data are needed to inform policy on the design and benefits of influenza vaccination. We set out to estimate the cost-effectiveness of seasonal influenza vaccination in Kenya. Methods: We fitted an age-stratified dynamic transmission model to active surveillance data from patients with influenza from 2010 to 2018. Using a societal perspective, we developed a decision tree cost-effectiveness model and estimated the incremental cost-effectiveness ratio (ICER) per disability-adjusted life year (DALY) averted for three vaccine target groups: children 6-23 months (strategy I), 2-5 years (strategy II) and 6-14 years (strategy III) with either the Southern Hemisphere influenza vaccine (Strategy A) or Northern Hemisphere vaccine (Strategy B) or both (Strategy C: twice yearly vaccination campaigns, or Strategy D: year-round vaccination campaigns). We assessed cost-effectiveness by calculating incremental net monetary benefits (INMB) using a willingness-to-pay (WTP) threshold of 1-51% of the annual gross domestic product per capita ($17-$872). Results: The mean number of infections across all ages was 2-15 million per year. When vaccination was well timed to influenza activity, the annual mean ICER per DALY averted for vaccinating children 6-23 months ranged between $749

Rapid Assessment of the Potential Paucity and Price Increases for Suggested Medicines and Protection Equipment for COVID-19 Across Developing Countries With a Particular Focus on Africa and the Implications

“…More specific data on actual changes in utilisation and prices was asked if this was available; however, this did not include asking the pharmacists to break down changes in utilisation patterns and prices per month as this was deemed too problematic for this initial study. In addition, it was envisaged there would be limited impact of seasonality in view of year-round influenza activity in some African countries and no real pattern in others ( WHO, 2012 ; Dawa et al, 2020 ; WHO Regional Office for Africa, 2020 ) although research is ongoing in this area to address current knowledge gaps ( Sambala et al, 2018 ). In addition, generally limited use of hydroxychloroquine in immunological diseases such as rheumatoid arthritis with concerns over its effectiveness compared with other disease modifying therapies ( Rempenault et al, 2020 ).…”

Potential health and economic impact of paediatric vaccination using next generation influenza vaccines in Kenya: a modelling study

“…Our analyses demonstrate the importance of assumed cost-effectiveness thresholds when determining whether health interventions are cost-effective or not. Kenya does not have an official cost-effectiveness threshold, but Dawa et al (2020) reported that vaccination with current seasonal influenza vaccines in Kenya had a low probability of being cost-effective given WTP thresholds of 1-51% of per capita GDP. To address uncertainty around thresholds, we used a wide range of values ranging from extremely low WHO "best buys" threshold reserved for evaluating some of the most cost-effective programmes that WHO has ever evaluated (21), to very high 1-3 times GDP per capita thresholds representing the potential value of human capital associated with disability (24).…”

“…A key strength of our epidemiological model is the direct incorporation of vaccine-derived immunity waning over multiple years, with ageing of the population, which is required to evaluate next generation vaccines with benefits that last several years. This contrasts to many seasonal vaccination models where vaccine-derived immunity is not tracked across seasons (2,13). In contrast with the marked annual seasonality of influenza in temperate regions (27), influenza epidemics in Kenya do not have a regular seasonal pattern, with substantial transmission in between epidemics, which we included by separately modelling the inter-epidemic periods.…”

“…Influenza is a major cause of respiratory illness in Kenya, particularly in children under 5 years old (1,2). Current influenza vaccines result in short-term, strain-specific immunity (3) which is particularly problematic in tropical and subtropical settings where multiple peaks and identifiable year-round activity make it challenging to decide if, who and when to vaccinate, as well as which formulation (northern or southern hemisphere) to use (4)(5)(6)(7).…”

“…Where an epidemic was previously defined to last less than 8 months, we follow it for the full 8 months to allow capturing the consequences of a slower epidemic progression as the result of vaccination. At the start of each epidemic the proportion of the population in the S, Sv and Rv compartments is taken from the output of the vaccination model, in the matching week and for the relevant virus subtype.Vaccine efficacy is split into NH and SH time frames as in the vaccination model.For each epidemic we run an independent transmission model (with structure of Figure1B) with the estimated transmission rate, susceptibility for three age groups (<= 14, 15-49, 50+), initial number of infections and the probability of identifying an influenza-positive patient within the catchment population for 3 age groups (<1, 1-5, 6+) fromDawa et al (2020).Influenza immunity is assumed to be leaky. Supplement section 2 contains the model equations, parameters and values.For key transmission parameters (transmission rate, susceptibility, number of infections at the start of the season, number of imports and ascertainment rates), we use the estimated values by Dawa et al 2020 for each of the 11 strain/subtype-specific peaks in influenza activity identified between 2010 -2018 (input 2).…”