Health impact and cost-effectiveness of vaccination using potential next-generation influenza vaccines in Thailand: a modelling study

Abstract

Introduction: Thailand was one of the first low- and middle-income countries to publicly fund seasonal influenza vaccines, but the lack of predictability in the timing of epidemics and difficulty in predicting the dominant influenza subtypes present a challenge for existing vaccines. Next-generation influenza vaccines (NGIVs) are being developed with the dual aims of broadening the strain coverage and conferring longer-lasting immunity. However, there are no economic evaluations of NGIVs in Thailand.

Methods: We estimated the health impact and cost-effectiveness of NGIVs in Thailand between 2005 and 2009 using a combined epidemiological and economic model. We fitted the model to data on laboratory-confirmed influenza cases and then simulated the number of influenza infections, symptomatic cases, hospitalisations and deaths under different vaccination scenarios based on WHO-preferred product characteristics for NGIVs. We used previous estimates of costs and disability adjusted life years (DALYs) for influenza health outcomes to estimate incremental net monetary benefit, vaccine threshold prices and budget impact.

Results: With the current vaccine programme, there were an estimated 61 million influenza infections. Increasing coverage to 50% using improved vaccines reduced infections to between 23 and 57 million, and with universal vaccines to between 21 and 49 million, depending on the age groups targeted. Depending on the comparator, threshold prices for NGIVs ranged from US$2.80 to US$12.90 per dose for minimally improved vaccines and US$24.60 to US$69.90 for universal vaccines.

Conclusion: Influenza immunisation programmes using NGIVs are anticipated to provide considerable health benefits and be cost-effective in Thailand. However, although NGIVs might even be cost-saving in the long run, there could be significant budget implications for the Thai government even if the vaccines can be procured at a substantial discount to the maximum threshold price.

Keywords: Global Health; Health economics; Immunisation; Respiratory infections; Vaccines.

Figure 1. Overview of modelling framework and transmission model structure adapted from Waterlow et al. (A) Flowchart showing the combined vaccination, transmission and economic model used in the analysis. Orange shows inputs to each part of the model, and brown shows the outputs from each step. (B) The transmission model used in this work is stratified by age (1) and influenza strain (k) and has two arms, representing unvaccinated and vaccinated groups. The E and I compartments have two sequential compartments to model Erlang (gamma) delay distributions. DALY, disability adjusted life year; FOI, force of infection.

Figure 2. Cost-effectiveness plane showing incremental costs and incremental DALYs averted for different next-generation influenza vaccine types under different coverage scenarios compared to the existing coverage of current vaccines. Dashed lines show the guideline cost-effectiveness threshold of 160 000 Baht per DALY averted. DALY, disability adjusted life year.

Figure 3. Incremental net monetary benefit of different next-generation influenza vaccine types and coverage scenarios compared to existing coverage of current vaccines.

Figure 4. Annual budget impact of different vaccine types and different age targeting strategies under the assumption that different vaccines are priced at a similar discount relative to the estimated threshold price as current vaccines.