Table 3 shows the main results of the analysis, including DALYs averted, costs, average cost effectiveness ratio, and incremental cost effectiveness for all interventions in both the sub-Saharan African sub-region (Afr-E) and south east Asian sub-region (Sear-D). To allow greater comparability with interventions in other disease areas, we standardised both cost and effectiveness estimates in relation to regional population size. Effectiveness results are expressed in the number of DALYs averted per million population per year of implementation of the intervention. Cost results are expressed in millions of international dollars per million population per year, which is equivalent to the cost per capita.
Table 3 Costs, effects, and cost-effectiveness of interventions to combat asthma and chronic obstructive pulmonary disease (COPD) in WHO sub-Saharan African sub-region AfrE and South East Asian sub-region SearD
Population level effect of interventions
The magnitude of impact of each intervention is different between the two regions. For example, in the sub-Saharan African sub-region all asthma interventions are noticeably more cost effective than all COPD interventions. The case is somewhat different in the South East Asian sub-region, where one COPD intervention (flu vaccine) is competitive with asthma interventions because of the higher underlying burden of COPD in that region. However, the relative order of effectiveness between regions is similar: inhaled bronchodilator (for COPD stage II) is the most effective intervention in both regions, averting 58 DALYs per million population per year of intervention in Afr-E and 370 DALYs in Sear-D; the next most effective in the Afr-E is low dose inhaled corticosteroids plus long acting β agonists for moderate persistent asthma cases, averting 45 DALYs, whereas in Sear-D the next is inhaled bronchodilator and corticosteroid (for COPD stage III and IV), which averts 151 DALYs (equivalent to 41%–76% of the inhaled bronchodilator (COPD stage II) intervention).
Influenza vaccine in the sub-Saharan African sub-region and medium dose inhaled corticosteroids for moderate persistent asthma cases in the South East Asian sub-region are least effective of the interventions analysed, producing only about 1%–7% of the number of DALYs averted by the use of inhaled bronchodilator (COPD stage II) in both regions. Part of the explanation for this relatively small impact is that flu vaccine is expected to have no impact on COPD associated disability, whereas use of long term anticholinergic bronchodilator is expected to reduce COPD associated disability by up to 97%, as measured by St George’s Respiratory. Questionnaire.38
Population level cost of interventions
The annual costs of interventions per million population ranged from $Int49
000 to $Int749
000 in the sub-Saharan African sub-region and from $Int12
000 to $Int4
000 in the South East Asian sub-region (rounded to the nearest thousand). Cost estimates of most interventions were appreciably different across the two regions (table 3). In general, asthma interventions in the African sub-region were more costly than in the South East Asian sub-region because of the larger number of patients treated. The reverse was true with respect to COPD interventions—that is, COPD interventions reported higher costs in Sear-D than in Afr-E because of the high number of patients who could benefit from treatment in that region. The interventions inhaled bronchodilator (for COPD stage II), inhaled bronchodilator and corticosteroid (COPD stage III and IV), and oxygen therapy (COPD stage IV), which are based on the administration of drugs, cost five times less in the sub-Saharan African sub-region than in the south east Asian sub-region. The cost per capita per year of influenza vaccine was about the same in both regions.
There is substantial variation of population level cost of interventions, ranging from a few cents per capita for low dose inhaled corticosteroids given to patients as step 2 asthma treatment to more than $Int4 per capita for inhaled bronchodilator (for COPD stage II and III) in the South East Asian sub-region.
In terms of cost breakdown, patient level costs are the main cost component for most COPD interventions in both regions, reflecting the high cost of drugs. The treatment of severe COPD exacerbations also had a considerable cost (about 62%) resulting from the provision of hospital bed days. For the provision of oxygen therapy, inhaled bronchodilators, and corticosteroids, patient level costs can account for more than 90% of total costs. For asthma interventions with more than one drug—namely inhaled corticosteroids plus long acting β agonists and inhaled corticosteroids plus leukotriene receptor agonists—primary care visits accounted for 24% of the total cost of these interventions, while the drugs accounted for the remaining 76% of costs. For the other interventions (low and medium dose inhaled corticosteroids), these proportions were inverted, with primary care visits and drugs accounting for 76% and 24% of costs, respectively.
Cost effectiveness of interventions
The combined analysis of both costs and effects shows the relative cost effectiveness of the interventions (figs 1 and 2). The cost per DALY averted for all interventions analysed ranged from $Int2686 to $Int39
307 in the sub-Saharan African region and from $Int2420 to $Int50
651 in the South East Asian region.
Fig 1 Cost effectiveness isoquants of interventions for chronic obstructive pulmonary disease (COPD) and asthma interventions (at 80% coverage) for sub-Saharan African sub-region Afr-E. See table 3 for explanation of intervention codes
Fig 2 Cost effectivenes isoquants of chronic obstructive pulmonary disease (COPD) and asthma interventions (at 80% coverage) for South East Asian sub-region Sear-D. See table 3 for explanation of intervention codes
In both regions, low dose inhaled corticosteroids for mild persistent asthma was the most cost effective intervention, costing an estimated $Int2420 (Sear-D) and $Int2686 (Afr-E) per DALY averted. If more resources were to become available, the incremental cost effectiveness ratio can be used to assess each intervention in relation to the preceding most preferred intervention. In the sub-Saharan African region, the next preferred interventions on the basis of cost effectiveness were low dose inhaled corticosteroids plus long acting β agonists for moderate persistent asthma (incremental cost effectiveness ratio $Int9112 per DALY averted) and next, inhaled bronchodilator for COPD stage II ($Int36
769 per DALY averted). In the South East Asian region, the next preferred interventions were influenza vaccine for COPD ($Int4950 per DALY averted) and inhaled bronchodilator for COPD stage II ($Int11
694 per DALY averted).
The other interventions have considerably higher cost effectiveness ratios (table 3). For example, inhaled bronchodilator and corticosteroid (COPD stages III and IV) costs $Int13
000 per DALY averted, while treatment of severe exacerbations costs around $Int18
000 per DALY averted in sub-Saharan Africa and $Int9000 in South East Asia. The cost effectiveness ratio of oxygen therapy is almost $Int40
000 per DALY averted in sub-Saharan Africa region and in excess of $Int50
000 per DALY averted in the South East Asian region.
The results of this analysis suggest that, if funds are available, both regions should first implement provision of low dose inhaled corticosteroids for mild persistent asthma. Over 10 years, this intervention would avert 100
239 DALYs at a cost around $Int269m in the sub-Saharan African region and 67
000 DALYs at a cost around $Int162m in South East Asian region.
The baseline effectiveness results in table 1 allow for discounting of health benefits at the rate of 3% per year and also apply age specific weights, giving relatively more importance to health gains in middle adult age as opposed to younger and older ages. To examine the importance of these sources of model uncertainty, the model was re-estimated first without the age weights and then without both the age weights and the discount factor. In both cases results were found to be sensitive to the specification of the effectiveness measure. Relaxing the age weighting assumption increased up to 64% the number of DALYs averted (since health gains are in older populations), while eliminating the rate of discount increased benefits up to 113% (since health gains are not realised immediately). As a consequence, cost effectiveness ratios were reduced by up to 39% with the elimination of age weighting and by up to 53% with the elimination of both age weighting and discounting. Influenza vaccine and oxygen therapy were relatively more affected among the interventions examined. This implies that the baseline results should be interpreted as conservative estimates of the cost effectiveness ratio.
A key parameter of the smoking cessation intervention was the prevalence of smoking among people with diagnosed COPD. As this information was not available for all regions, sensitivity analysis was performed by halving the baseline scenario values for this parameter in each region. Sensitivity analysis results are similar in both regions. The total implementation cost is not affected significantly, but the number of DALYs averted is reduced by about 50% and the cost effectiveness ratio doubles as the number of potential cases treated is reduced.
The probabilistic uncertainty analysis depicted in figures 3 and 4 shows the impact of plausible variations in total costs and total effects and shows that the average cost effectiveness ratio of most interventions would retain a classification of “cost effective” or “not cost effective” after variation around the point estimates was taken into account. A similar logic would apply to the incremental cost effectiveness ratios. Concerning low dose inhaled corticosteroids plus long acting β agonists for moderate persistent asthma (intervention code AST-2) in the South East Asian sub-region, however, figure 3 shows that a substantial part of the probability distribution for its average cost effectiveness estimate would lie outside of the region considered cost effective.
Fig 3 Probabilistic uncertainty graph of interventions for chronic obstructive pulmonary disease (COPD) and asthma interventions (at 80% coverage) for sub-Saharan African sub-region Afr-E. See table 3 for explanation of intervention codes
Fig 4 Probabilistic uncertainty graph of interventions for chronic obstructive pulmonary disease (COPD) and asthma interventions (at 80% coverage) for WHO South East Asia sub-region SearD. See table 3 for explanation of intervention codes