A budget impact analysis of adult immunization with tetanus, diphtheria, and pertussis vaccination for the prevention of pertussis in at-risk populations in Colombia

ABSTRACT

Pertussis (i.e. whooping cough) is an acute respiratory disease that can cause substantial morbidity and healthcare costs. Patients at higher risk of pertussis may benefit from booster vaccination (Tdap). This study aimed to estimate the budget impact of introducing Tdap into Colombia’s healthcare insurance plan (HCIP) for at-risk adults (asthma, COPD, and HIV) aged ≥ 20 years. For each population, a Microsoft Excel-based model was developed with a five-year time horizon. Demographic inputs were obtained from the United Nations Department of Economic and Social Affairs and the World Bank Group. Epidemiology inputs were from peer-reviewed retrospective studies and systematic reviews of pertussis. Cost inputs were based on 2023 pricing data indexed to consumer price indices. Tdap coverage and market share were assumed as 10% and 74%, respectively. Without Tdap, estimated total five-year medical costs associated with pertussis disease management, in United States dollars ($), were $34.6 million (M), $37.4 M, and $9.3 M, for patients with asthma, COPD, and HIV. Introducing Tdap could avoid 135, 103, and 50 pertussis cases and 8, 9 and 3 hospitalizations due to pertussis in these populations. The total budget impact of Tdap entry into Colombia’s HCIP was $1.3 M, $1.2 M and ~$137 thousand for patients with asthma, COPD, and HIV, respectively. Therefore, introducing Tdap vaccination for adults with asthma, COPD, and HIV in Colombia at just 10% coverage could substantially decrease pertussis disease burden and associated healthcare resource utilization. A proportion of the HCIP budget would be required to protect those at risk.

Introduction

Pertussis, commonly known as whooping cough, is an acute respiratory disease caused by the bacterium Bordetella pertussis.¹ It is characterized by a violent and rapid coughing, coupled with rapid expulsion of air from the lungs, which lasts for 3–8 weeks in adolescents and adults.¹ Although pertussis is mainly considered a pediatric disease, it is an important cause of illness in adolescents and adults.^1,2

Despite the incidence of pertussis having declined in recent history, a considerable number of pertussis cases are still reported annually. According to the World Health Organization (WHO), in 2023 the global incidence rate of pertussis was 23.6 per 1 million population, equaling almost 160,000 reported cases.³ In Colombia, WHO-reported pertussis incidence rates have fluctuated over the past decade, generally decreasing from 15.8 per 1 million population in 2014 to 1.0 per 1 million population in 2023.⁴ This downward trend is largely attributed to the implementation of pertussis immunization programs and improved vaccination coverage across many parts of the world.⁵ However, pertussis cases are thought to be widely underreported in Latin America, particularly among adults, with a 2023 study estimating that the number of pertussis cases among adults ≥50 years in Argentina, Brazil, Chile, Mexico and Peru is approximately 104–114 times higher than the number reported to national surveillance systems.⁶ Globally, an increasing number of reported pertussis cases involve older children and adults, particularly for cases resulting in hospitalization in older adults.^1,2,7 Furthermore, pertussis infection in adults is associated with significant healthcare resource utilization and associated costs, and a reduction in quality of life.²

Several risk factors have been previously identified for pertussis infection and severity in adults, including older age, and underlying conditions, including asthma and coronary obstructive pulmonary disease (COPD).^8,9 For example, in a study of 205 laboratory-confirmed pertussis cases among adults aged ≥45 years in Australia, a history of preexisting asthma was identified as a significant predictor of pertussis incidence.¹⁰ A 2015 case-control study in Iran found that a significantly higher proportion of adults with COPD had indication of recent pertussis infection compared to matched controls without COPD.¹¹ Previous studies have also indicated that pertussis can lead to increased exacerbation of underlying respiratory conditions,^8,9 which may be due to the contribution of pertussis to the degradation of the respiratory tract,¹² although the exact mechanism for this exacerbation requires further investigation. Furthermore, the greater likelihood of patients with underlying conditions developing complications associated with pertussis can lead to increased healthcare costs.¹³ Adults with such underlying conditions may therefore be considered to be “at-risk” of pertussis, and preventing pertussis infection in these populations can help to reduce the overall burden of pertussis on patients and healthcare systems. Despite this, several articles across multiple regions globally have identified a general lack of awareness among healthcare professionals of the risk of pertussis in adults and an underestimation of the need to protect adults from the disease.^14–16 Furthermore, a 2020 report on risk management among people with chronic respiratory conditions in Colombia found particularly low vaccination rates among at-risk populations, with vaccination rates for both influenza and pneumococcal disease of just 1% and 0.1% among adults with COPD and asthma, respectively.¹⁷

Vaccination against pertussis is generally included in national immunization programs globally, particularly for children and adolescents, with the WHO recommending routine pertussis immunization for children and pregnant individuals.¹⁸ However, protection against pertussis is not lifelong due to waning immunity,¹⁹ with booster vaccination shown to be an effective and safe method of pertussis prevention in vulnerable populations, including older adults.²⁰

Multiple vaccines are indicated for booster immunization for pertussis, including the combined tetanus, diphtheria, acellular pertussis vaccine with three pertussis components (Boostrix^Ⓡ, GlaxoSmithKline; hereafter referred to as Tdap) and the combined tetanus, diphtheria, acellular pertussis vaccine with five pertussis components (Adacel^Ⓡ, Sanofi Pasteur; hereafter referred to as Tdap5).²¹ Tdap is presented as a suspension for injection in 0.5 mL single dose, prefilled syringes and, in Colombia, it is currently recommended by the Ministry of Health for adults with human immunodeficiency virus (HIV), but not other at-risk populations such as adults with asthma and COPD.^22,23 Tdap is also not included in the Colombian national immunization program for any of these three populations, despite its recommendation in adults with HIV.

However, various barriers and facilitators to booster vaccination uptake have been previously identified in studies across Latin America. For example, a recent cross-sectional study identified family income, religious beliefs, vaccine safety concerns, and perceived vaccine importance as significant barriers to coronavirus disease 2019 (COVID-19) booster vaccine acceptability in Brazil.²⁴ Additionally, a systematic review of vaccination acceptance in Latin America identified recommendations from health professionals and positive experiences with health services as two facilitators to vaccination, while barriers to vaccination included a lack of information, structural issues with healthcare services, safety concerns, and financial issues for patients.²⁵ Finally, a study of immunization practices in adults in older age groups in Colombia found lack of recommendation from healthcare providers, lack of coverage in national immunization campaigns, and fear of adverse effects to be the three largest barriers to immunization.²⁶

In Colombia, the national immunization program is largely centrally-funded and provides vaccines free-of-charge to target populations.²⁷ Formal prescriptions for vaccines are not mandatory and, provided the vaccine is recommended by a physician in line with its approved indication, vaccines are administered to patients as requested. No specific guidelines exist regarding which healthcare professional should recommend vaccines in Colombia and at what level of care vaccines should be administered. However, as mentioned, lack of coverage in national immunization campaigns is a barrier to immunization and the recommendation rate for certain vaccines, including Tdap, in populations not included in the national immunization program in Colombia has been demonstrated to be low.²⁶ Incorporating booster vaccinations into national immunization programs is therefore one potential method for increasing uptake and protection for vulnerable populations. It is therefore important to assess the impact of Tdap booster vaccination for additional at-risk adult populations in Colombia, beyond those covered in current Ministry of Health recommendations, to determine how its national immunization program could be expanded.

The objectives of this study were to estimate the budget impact of introducing Tdap into Colombian national immunization programs to prevent pertussis in at-risk adult populations (patients with asthma, COPD, and HIV) aged ≥20 years, from a payer perspective. To the authors’ knowledge, this study is the first of its kind to report budget impact data in these Colombian populations. Having this information will allow the Colombian Ministry of Health to assess the cost implications, and therefore feasibility, of introducing Tdap for additional at-risk populations in Colombia, and enable them to consider expanding their pertussis immunization schedule within the adult population.

Methods

Model design

A Microsoft Excel-based budget impact model was developed to estimate the budget impact, from a payer perspective, of introducing Tdap as a booster vaccine at 20 years old into national immunization in Colombia among adults with asthma, COPD or HIV, who are at-risk of severe pertussis (Figure 1). The budget impact is assessed separately for each high-risk group over five years following Tdap entry, spanning 2025 to 2029.

Figure 1.

Model structure.

Abbreviations: Tdap: tetanus-diphtheria-acellular pertussis vaccine.

In the base case, the impact of introducing Tdap booster vaccination was compared to a scenario where the whole target population was assumed to be unprotected and susceptible to a pertussis infection.

Model inputs

Demographics

The base population included adults aged ≥20 years residing in Colombia with either asthma, COPD or HIV (Table 1). Age distribution was taken from population pyramids reported by the United Nations Department of Economic and Social Affairs in 2021,²⁸ and annual population growth was obtained from the World Bank Group (1.1%).²⁹

Table 1.

Demographic, epidemiology, and vaccine information model inputs.

Age cohort, years	20–29	30–39	40–49	50–59	60–69	70–79	80–89	90–99
Demographic inputs
2021 population size, n (%)28	8,967,151 (17)	8,213,053 (16)	6,614,027 (13)	5,730,298 (11)	3,994,662 (8)	2,017,405 (4)	676,597 (1)	74,670 (0)
Annual population growth, %29	1.1%
Epidemiological inputs
Pertussis incidence30	5.35 per 100,000
Pertussis reporting rate, %30,31	11.6	11.6	7.5	3.4	3.4	3.4	3.4	3.4
Pertussis severity (%)32–34
Mild	11	11	11	11	13	14	14	14
Moderatea	86	86	86	86	80	74	74	74
Severe	3	3	3	3	8	12	12	12
Pertussis hospitalization rate (%)36,b	Severe cases: 100
Pertussis mortality rate (%)36	Severe hospitalized cases: 0.86
Prevalence of UCs (%)
Asthma37	6.3
COPD39	2.5	4.6	2.8	5.9	12.4	25.3	25.3	25.3
HIV38	1.9	2.9	1.8	1.4	0.6	0.6	0.6	0.6
Relative risk of pertussis, n (95% CI)
Asthma13	4.1 (3.9–4.3)c				3.2 (2.7–3.9)d
COPD13	3.6 (3.4–3.8)c				1.9 (1.6–2.1)d
HIV40	14.0 (3.9–4.3)c				14.0 (2.7–3.9)d
Vaccine-related inputs
Mean vaccine efficacy, % (Upper, Lower)42
Tdap	52 (15, 73)
Tdap5	52 (15, 73)
Vaccine market share, %41
Tdap	74
Tdap5	26
2023 vaccine price, USD43,44
Tdap	14.63
Tdap5	14.96

[a] Proportions of patients with moderate pertussis were based on the remaining proportion when mild and severe cases were removed; [b] Hospitalization rates were assumed to be 100% for all severe cases; [c] Includes patients aged 19–64 years; [d] Includes patients aged ≥65 years. Abbreviations: CI: confidence interval; COPD: coronary obstructive pulmonary disease; HIV: human immunodeficiency virus; Tdap: tetanus-diphtheria-acellular pertussis vaccine; Tdap5: tetanus-diphtheria-acellular pertussis (5 components) vaccine; UC: underlying condition; USD: United States dollar.

Epidemiology

Annual pertussis incidence per 100,000 population was calculated via the average of overall incidence rates reported in 2011 and 2012 in a retrospective study of Brazilian surveillance data (5.4 per 100,000).³⁰ Additional epidemiology inputs among the general population included pertussis reporting rate split by age group, taken from a 2015 retrospective study of pertussis incidence in Brazil and a systematic review of pertussis epidemiology in Latin America,^30,31 and proportion of patients with different pertussis severity (mild, moderate or severe) (Table 1).^32–34 Proportions of patients with mild and severe pertussis were based on previously reported rates of patients without a paroxysmal cough and previous hospitalization rates, respectively.^32–34 Proportions of patients with moderate pertussis were based on the remaining proportion when mild and severe cases were removed. Hospitalization and mortality rates of pertussis were also inputted (Table 1); hospitalization rates were assumed to be 100% for all severe cases,³⁵ while mortality rates were obtained from inputs used in a 2015 United States (US) cost-effectiveness study of Tdap vaccination in adults aged ≥65 years due to a lack of available mortality data for Colombia.³⁶

Asthma, COPD, and HIV prevalence data were taken from three cross-sectional studies in Colombia conducted between 2008–2019 (Table 1).^37–39 Relative risk of pertussis infection amongst patients with asthma, COPD, and HIV were selected from a retrospective administrative claims analysis among individuals with asthma and COPD,¹³ and an analysis of stored serum samples among individuals with HIV,⁴⁰ both of which were US-based.

Vaccine coverage, market share and efficacy

The assumed booster dose coverage for Tdap was conservatively set at 10% of the at-risk population (adults with asthma, COPD, or HIV). Tdap market share was set to 74%, with the remaining 26% being allocated to Tdap5, and was based on data from the Integrated System of Information of Social Protection (SISPRO) database.⁴¹

Vaccine efficacy rates against pertussis were calculated on the basis of data taken from a case-control study of vaccination efficacy against pertussis in adults aged ≥45 years (52%; Table 1).⁴² Vaccine efficacy was assumed to be the same across all three at-risk populations. Waning effect decay was assumed to be 5% per year.

Costs

A summary of the inputted cost data is provided in Supplementary Table S1. Vaccine-related costs were calculated based on 2023 pricing data indexed in consumer price indices, and included acquisition and administration costs.^43,44

Pertussis-related disease management costs included costs associated with diagnostic tests, treatments, primary care visits, and outpatient complications (including pneumonia, seizure, and encephalopathy).⁴⁴

Costs associated with treating underlying conditions were sourced from three cost-of-illness studies of each disease in Colombia.^45–47

Model outputs

The number of pertussis cases, complicated outpatient pertussis cases, pertussis-related hospitalizations, and deaths were estimated for each at-risk population, with and without Tdap entry as a booster into Colombia’s healthcare insurance plans. The number of Tdap vaccinations administered is also reported.

Cost outcomes were also assessed for each at-risk population, with and without Tdap entry, and included total vaccination costs (A), costs associated with pertussis treatment (B), and costs associated with treating underlying conditions (C). The net total budget impact of Tdap entry as a booster into Colombia’s healthcare insurance plans was calculated via the sum of the net difference in B and C with versus without Tdap entry, and A.

Cost outcomes were originally calculated in Colombian pesos and are reported here in 2023 US dollars (USD; 1 US dollar = 4,332.24 Colombia peso).⁴⁸

Sensitivity analyses

A deterministic sensitivity analysis (DSA) was performed to assess the robustness of base case inputs included in the study. Each model input was adjusted from the base case value, using prespecified ranges based on the uncertainty in each input in the source data, to evaluate the relative impact on the estimated total budget impact of Tdap entry.

Scenario analyses

Scenario analyses were performed by altering model assumptions to explore the impact of increasing the market share of Tdap to 100% on model outputs.

Ethics

The model was based on previously conducted studies and does not contain any new studies with human participants or animals performed by any of the authors.

Results

Base case results

Pertussis cases, outpatient complications, and hospitalizations

For at-risk individuals aged ≥20 years included in the base case analysis of the model, without Tdap entry as a booster into Colombia’s healthcare insurance plans, there would be total of 33,662, 24,567, and 10,023 pertussis cases over the over the 5 year period for patients with asthma, COPD, and HIV, respectively (Figure 2a). In this same scenario, there would be 3,257, 2,323, and 975 outpatient pertussis cases with complications, 1,903, 2,074, and 509 pertussis-related hospitalizations, and 12, 9, and 3 pertussis-related deaths (Figure 2b–d).

Figure 2.

Pertussis-related health outcomes with and without Tdap entry as a booster into Colombia’s healthcare insurance plans, for adults with asthma, COPD, or HIV.

(a) Pertussis cases

(b) Outpatient pertussis cases with complications

(c) Pertussis-related hospitalizations

(d) Pertussis-related deaths.

Abbreviations: COPD: coronary obstructive pulmonary disease; HIV: human immunodeficiency virus; Tdap: tetanus-diphtheria-acellular pertussis vaccine.

Introducing Tdap entry as a booster into Colombia’s healthcare insurance plans at 10% coverage with a 74% market share could avoid approximately 135, 103, and 50 of these pertussis cases for patients with asthma, COPD, and HIV, respectively (Figure 2a). Additionally, 13, 10, and 5 outpatient pertussis cases with complications, and 8, 9, and 3 pertussis-related hospitalizations could be avoided (Figure 2b–d). In this scenario, no deaths were avoided across the three populations.

Costs and budget impact

Costs associated with pertussis disease management over the 5 year period, without Tdap entry as a booster into Colombia’s healthcare insurance plans, were estimated to be $34.6 million (M), $37.4 M, and $9.3 M for patients with asthma, COPD, and HIV, respectively (Figure 3a; Table 2). Costs associated with treating complications of underlying conditions (asthma, COPD, and HIV) were $1.9 M, $19.3 M, and $21.6 M, respectively (Figure 3b; Table 2).

Figure 3.

Pertussis-related medical costs with and without Tdap entry as a booster into Colombia’s healthcare insurance plans, for adults with asthma, COPD, or HIV.

(a) Total medical costs associated with pertussis disease management

(b) Total costs associated with treating UCs^a

[a] Costs associated with treating exacerbation of asthma and COPD due to pertussis, and costs associated with treating HIV. Abbreviations: COPD: coronary obstructive pulmonary disease; HIV: human immunodeficiency virus; M: million; Tdap: tetanus-diphtheria-acellular pertussis vaccine; UC: underlying condition USD: United States dollar.

Table 2.

Total pertussis-related medical costs with and without Tdap entry as a booster into Colombia’s healthcare insurance plans.

	Without Tdap entry (A)	With Tdap entry (B)	Difference (B – A)
Number of vaccinations administered, n
Asthma	0	99,387	99,387
COPD	0	101,691	101,691
HIV	0	19,869	19,869
Vaccination costs, USD
Asthma	0	1,454,357.42	1,454,357.42
COPD	0	1,488,075.34	1,488,075.34
HIV	0	290,751.83	290,751.83
Total costs of pertussis disease management, USD
Asthma	34,559,285.30	34,417,432.03	−141,853.27
COPD	37,383,116.01	37,218,559.03	−164,556.98
HIV	9,264,799.54	9,218,530.79	−46,268.74
Total costs associated with treating UC,a USD
Asthma	1,905,779.55	1,898,126.57	−7,652.98
COPD	19,291,506.51	19,210,661.43	−80,845.08
HIV	21,607,753.34	21,500,735.08	−107,018.26
Total direct pertussis-related medical costs, USD
Asthma	36,465,064.85	37,769,916.02	1,304,851.17
COPD	56,674,662.53	57,917,295.81	1,242,673.28
HIV	30,872,552.88	31,010,017.71	137,464.83
Total direct pertussis-related medical costs per vaccinated individual, USD
Asthma	N/A	380.03	N/A
COPD	N/A	569.54	N/A
HIV	N/A	1,560.70	N/A
Total budget impact, USD
Asthma	1,304,851.17
COPD	1,242,673.28
HIV	137,464.83

[a] Costs associated with treating exacerbation of asthma and COPD due to pertussis, and costs associated with treating HIV. Abbreviations: COPD: coronary obstructive pulmonary disease; HIV: human immunodeficiency virus; N/A: not applicable; Tdap: tetanus-diphtheria-acellular pertussis vaccine; UC: underlying condition; USD: United States dollar.

Introducing Tdap entry as a booster into Colombia’s healthcare insurance plans for patients with asthma, COPD, and HIV was estimated to require 99,387, 101,691, and 19,869 vaccinations across the five-year period, respectively (Table 2). Vaccination costs were estimated to be $1.5 M, $1.5 M, and ~$291 thousand (K) for asthma, COPD, and HIV, respectively.

Tdap entry was estimated to reduce costs associated with pertussis disease management by ~$142 K, ~$165 K, and ~$46 K in patients with asthma, COPD, and HIV, respectively (Figure 3a; Table 2). Costs associated with treating underlying conditions reduced by ~$8 K, ~$81 K, and ~$107 K (Figure 3b; Table 2).

Total budget impact in direct medical costs to vaccinate 10% of at-risk populations were $1.3 M, $1.2 M, and ~$137 K across the five-year period for patients with asthma, COPD, and HIV, respectively (Figure 4; Table 2). Total budget impact estimates for each of the five years are provided in Table 3.

Figure 4.

Total budget impact of direct medical costs of Tdap entry as a booster into Colombia’s healthcare insurance plans for adults with asthma, COPD, or HIV.

Abbreviations: BI: budget impact; COPD: coronary obstructive pulmonary disease; HIV: human immunodeficiency virus; M: million; Tdap: tetanus-diphtheria-acellular pertussis vaccine; USD: United States dollar.

Table 3.

Total budget impact of Tdap entry as a booster into Colombia’s healthcare insurance plans by year.

	Incremental cost, USDa			Total budget impact
Year	Vaccination	Pertussis disease management	Treatment of UCs
Asthma
1	284,542.31	−27,753.33	−1,497.29	255,291.70
2	287,672.28	−28,058.61	−1,513.76	258,099.90
3	290,836.67	−28,367.26	−1,530.41	260,939.00
4	294,035.88	−28,679.30	−1,547.25	263,809.33
5	297,270.27	−28,994.77	−1,564.27	266,711.23
Total	1,454,357.42	−141,853.27	–7,652.98	1,304,851.17
COPD
1	291,139.16	−32,195.27	−15,817.19	243,126.71
2	294,341.69	−32,549.41	−15,991.18	245,801.10
3	297,579.45	−32,907.46	−16,167.08	248,504.91
4	300,852.83	−33,269.44	−16,344.92	251,238.47
5	304,162.21	−33,635.40	−16,524.71	254,002.09
Total	1,488,075.34	–164,556.98	–80,845.08	1,242,673.28
HIV
1	56,885.05	−9,052.39	−20,937.92	26,894.74
2	57,510.79	−9,151.97	−21,168.24	27,190.58
3	58,143.41	−9,252.64	−21,401.09	27,489.68
4	58,782.99	−9,354.42	−21,636.50	27,792.06
5	59,429.60	−9,457.32	−21,874.50	28,097.77
Total	290,751.83	–46,268.74	–107,018.26	137,464.83

[a] Incremental cost was calculated by subtracting the cost without Tdap entry from the cost with Tdap entry. Abbreviations: COPD: coronary obstructive pulmonary disease; HIV: human immunodeficiency virus; Tdap: tetanus-diphtheria-acellular pertussis vaccine; UC: underlying condition; USD: United States dollar.

Sensitivity analyses

In the DSA, the inputs with the largest impact on the total budget included number of Tdap doses (asthma: +22%, −22%; COPD: +24%, −24%; HIV: +42%, −42%), vaccine acquisition-related costs (asthma: +23%, −21%; COPD: +25%, −22%; HIV: +43%, −39%), and Tdap efficacy (asthma: +5%, −8%; COPD: +8%, −14%; HIV: +27%, −47%) for all three at-risk populations (Figure 5).

Figure 5.

Results of deterministic sensitivity analyses.

(a) Asthma

(b) COPD

(c) HIV.

In the DSA, model inputs were adjusted from the base case value, using prespecified ranges based on the uncertainty in each input in the source data, to evaluate the relative impact on the estimated total budget impact of Tdap entry. Abbreviations: COPD: coronary obstructive pulmonary disease; DSA: deterministic sensitivity analysis; GP: general practitioner; HIV: human immunodeficiency virus; ICU: intensive care unit; PCR: polymerase chain reaction.

Scenario analyses

Scenario analyses indicated that increasing market share of Tdap booster vaccine to 100% would result in a 35.1% increase in total budget impact over the 5 year period for all three at-risk populations assessed (Figure 6). These scenario analyses also resulted in an increase in the number of total pertussis cases, outpatient pertussis cases with complications, and hospitalization avoided across all three populations (Supplementary Table S2).

Figure 6.

Results of scenario analyses.

In the scenario analyses, the market share of Tdap was increased to 100%. Abbreviations: COPD: coronary obstructive pulmonary disease; HIV: human immunodeficiency virus; M: million; Tdap: tetanus-diphtheria-acellular pertussis vaccine; USD: United States dollar.

Discussion

In Colombia, national immunization programs for at-risk populations account for less than 1% of total government healthcare spending,⁴⁹ meaning it is important to evaluate the economic impact of introducing new vaccines into this program to determine feasibility. Overall, this study estimated that pertussis poses a substantial burden among at-risk adults in Colombia, and is a significant source of healthcare resource utilization, with total disease management costs over 5 years amounting to $34.6 M, $37.4 M, and $9.3 M USD for adults with asthma, COPD, and HIV, respectively. With an estimated requirement of 99,387, 101,691, 19,869 vaccinations, direct medical cost savings associated with introducing Tdap were estimated to be ~$142 K, ~$165 K, and ~$46 K in patients with asthma, COPD, and HIV, respectively. The total budget impact of introducing Tdap was predicted to be $1.3 M, $1.2 M, and ~$137 K for these same patient populations. As previously mentioned, to the authors’ knowledge, this is the first budget impact modeling exercise to assess the introduction of Tdap vaccination in at-risk adult populations in Colombia.

There is a scarcity of data available on the burden of pertussis in Colombia, making comparisons to previous literature difficult. This evidence gap may be due to patients often moving between healthcare institutions for treatment, resulting in inconsistent measurement of costs by payers. However, the high healthcare burden estimated in this study aligns with multiple previous studies of pertussis in adults with underlying conditions in other regions. For example, two individual retrospective database studies in England found pertussis infections among individuals with asthma and COPD to lead to a significant increase in direct medical costs, equaling £1,362 and £2,012 more per patient per year in the month prior to pertussis diagnosis, respectively, and £833 and £2,407 more in the two months following.^50,51 Although, to the authors’ knowledge, no previous studies have evaluated the economic impact of pertussis booster vaccination in at-risk adults, the cost-savings and budget impact values reported in this study align with a previous literature review of 13 health economic evaluations of pertussis booster vaccination in general adolescent and adult populations.⁵² This literature review found that all studies generally reached the same conclusion of pertussis booster vaccination being economically valuable.

Although data are limited for pertussis, considerable cost-savings associated with the introduction of booster vaccination programs have also been estimated for other respiratory diseases globally, with COVID-19 being a prominent example. Introducing a booster vaccination for COVID-19 among those aged ≥5 years in the US was estimated to yield $4.67 of cost-benefits for every $1 invested.⁵³ In Japan, the estimated vaccine-related costs of 1.39 trillion Japanese yen for annual COVID-19 booster vaccinations among those aged ≥60 years were anticipated to be offset by a 1.94 trillion Japanese yen reduction in productivity losses.⁵⁴ Finally, in Thailand, the total cost of introducing COVID-19 booster vaccination among those aged ≥12 years was far smaller than the total costs associated with a scenario where there was no booster, regardless of whether this booster was a viral vector vaccine or messenger ribonucleic acid (mRNA) vaccine (viral vector: 70 billion Thai baht; mRNA: 64.7 billion Thai baht; no booster: 109 billion Thai baht).⁵⁵ Although each concerned COVID-19, covered varying populations, and focused on different countries, making comparisons to the current study limited, in combination these studies all demonstrate the economic value of booster vaccinations for respiratory disease.

Without Tdap vaccination, a total of 33,662, 24,567, and 10,023 pertussis cases, and 1,903, 2,074, and 509 pertussis-related hospitalizations were predicted over five years, in patients with asthma, COPD, and HIV, respectively. Introducing Tdap vaccination with just 10% coverage could avoid 135, 103, and 50 pertussis cases and 8, 9, and 3 hospitalizations due to pertussis, in patients with asthma, COPD, and HIV, respectively. No deaths were avoided. Mortality in patients with pertussis and underlying conditions is often attributed to the underlying condition, with it being difficult to determine when pertussis is the true cause.⁵⁶ There was therefore a lack of mortality attributed to pertussis in the source data, which may explain the lack of deaths avoided in this study.

Scenario analyses predicted that increasing the market share of Tdap from 74% to 100% would result in a 35% increase in total budget impact over the 5 year period for all three at-risk populations assessed, indicating an increased financial commitment. However, it would also result in a greater number of total pertussis cases, outpatient pertussis cases with complications, and hospitalizations avoided. Additionally, sensitivity analyses identified that number of Tdap doses, vaccine acquisition-related costs, and Tdap efficacy had the largest impact on the estimated total budget impact for all three at-risk populations.

The results of this study should be interpreted within the context of its limitations. Firstly, the definition of ‘at-risk’ adults used in the study (i.e., adults with asthma, COPD, or HIV) does not capture all populations potentially at risk of pertussis infection and severe outcomes, such as adults in older age groups and those with obesity or immunocompromising conditions.^8,9,14 Additionally, lifestyle and societal factors such as smoking status and rurality have been previously associated with pertussis risk.^8,9,57 However, the at-risk populations investigated in this study were based on discussions with the Colombian Ministry of Health and therefore can be assumed to reflect the needs of policymakers within the country.

Moreover, the scarcity of available data related to pertussis epidemiology and Tdap vaccination in Colombia meant that several assumptions were applied to the model. For example, a lack of vaccine efficacy data in Colombia meant that efficacy inputs were based on a single case-control study of vaccination efficacy against pertussis in adults and was therefore assumed to be the same for both Tdap and Tdap5. This may have led to an overestimation or underestimation of patient health outcomes and cost outcomes, depending on the true vaccine efficacy in Colombia. Incidence data were also limited, meaning Brazilian data from 2011 and 2012, which were the most up-to-date data available at the time of the study that were comparable to Colombia, were incorporated into the model. Also, as the aim of this study was to estimate the impact of introducing Tdap into Colombian national immunization programs from a payer perspective, societal impacts such as reduced quality of life, lost workdays, and care costs were not incorporated into the model. Evaluating the impact of Tdap booster vaccination on society is an important additional consideration and presents an opportunity for future research.

Additionally, data related to vaccine coverage in Colombia was unavailable, meaning that the model input for this was based on assumption alone. However, the 10% coverage utilized in the model was a particularly conservative estimate, meaning overestimation of the impact of Tdap vaccination was unlikely. Data related to mortality rates in Colombia were also unavailable, meaning that data from the US were used in the model and may have led to an overestimation or underestimation of mortality outcomes, depending on the true mortality rate in Colombia. Furthermore, the base case compared the impact of introducing Tdap booster vaccination to a scenario where the whole target population was assumed to be unprotected and susceptible to a pertussis infection, which may have led to an overestimation of the outcomes reported. However, given the several barriers to vaccination in Latin America²⁵ and the fact that Tdap is not included in the national immunization program for adults with asthma, COPD, or HIV in Colombia, the authors expect actual rates of protection against pertussis in these populations to be low.

In addition, the study analyses were largely based on epidemiological data, and as previously mentioned, pertussis cases are likely underestimated in Latin America.⁶ This may have impacted the model estimates and could potentially have been overcome by using alternative data sources such as community registries or occupational health repositories. However, these data were unavailable at the time of conducting this study and recent reports have highlighted the risk of potential overestimation of pertussis cases from these data sources.⁵⁸ Finally, statistical analyses to confirm significance of the differences reported in the study were not performed, meaning it cannot be confirmed whether the differences in the data truly reflect the magnitude of the effect of introducing Tdap booster vaccination. Nevertheless, the results provide valuable insights into the potential cost implications of introducing Tdap booster vaccination for at-risk populations in Colombia, which can guide decision-making processes.

This study also has several strengths. Following the Professional Society for Health Economics and Outcomes Research (ISPOR) principles for good practice for budget impact analysis ensured that the study analyses were rigorous and reproducible.⁵⁹ Additionally, analyses of the impact of Tdap on medical costs were comprehensive, including how the medical costs associated with the treatment of underlying conditions could be averted. By accounting for both costs incurred and savings achieved, the results of this study allow decision-makers to fully evaluate the feasibility of implementing at-risk adult Tdap booster vaccination in Colombia’s healthcare insurance plans.

Overall, this study provides an indication of the burden of pertussis in at-risk populations in Colombia, and of the benefit that Tdap could bring to alleviate the occurrence of pertussis and costs associated with pertussis disease management. Pertussis is commonly underreported both globally and in Latin America, particularly among adolescents and adults who may present with atypical symptoms.^6,31 These results may therefore aid in improving awareness of the burden of pertussis in Colombia, with disease awareness being identified as a key factor for increasing vaccination acceptance amongst the public.^60,61

The benefits of implementing booster vaccination for at-risk populations are well-established across many disease areas, and the COVID-19 pandemic demonstrated the value of booster vaccination in vulnerable populations in particular.^62,63 Additionally, health inequality is a key issue in Colombia, with age, sex, income, and education being key drivers of disparities in health outcomes in the country.⁶⁴ Implementation of Tdap into national immunization programs would also allow all eligible individuals to have access to vaccination, reducing this inequality.

Conclusions

This study revealed that pertussis-related healthcare expenditure in Colombia for adult populations with asthma, COPD, or HIV is high, with exacerbation and treatment of these underlying conditions resulting in further healthcare costs. Introducing Tdap vaccination for at-risk populations in Colombia at just 10% coverage could substantially reduce pertussis disease burden and associated healthcare resource utilization. A moderate proportion of the national immunization budget over 5 years would be required to achieve this.

Despite some methodological limitations largely associated with assumptions applied to the model due to a lack of available data, this study provides meaningful insights into the impact of Tdap booster vaccinations for adults with asthma, COPD, and HIV in Colombia, which may aid Colombian policymakers in assessing the potential value of introducing Tdap into national immunization programs for at-risk adults. The findings may also help inform future research into the patient and healthcare burden of pertussis in Colombia, and aid in the development of vaccination campaigns to effectively communicate the benefit of Tdap, thus improving vaccine uptake.

Biography

Nurilign Ahmed holds a doctoral degree in Health Economics and Public Health from the London School of Hygiene and Tropical Medicine, London, UK. Her thesis centered on decision analytics and cost-effectiveness of HIV testing services in Zambia. During her doctoral work, she co-chaired the WHO’s cost-effectiveness of HIV testing services group. Post-PhD, she advised Rwanda’s and Zambia’s Health Ministries on essential medicine lists and worked with Africa CDC to establish a Health Economics Unit to support the African Union’s 54 member countries in evidence-based decision-making for healthcare priority setting. She has extensive experience across sub-Saharan Africa and led the CDC-US funded Couples HIV Testing program. Dr. Ahmed also has a Master of Public Health (MPH) in Global Health Infectious Disease from Emory University, Rollins School of Public Health, Atlanta, Georgia, USA and a BSc in Molecular and Neurobiology from the University of Wisconsin Madison, Wisconsin, USA. Since 2022, she has been an Associate Director at GSK, leading health outcomes studies for vaccines in emerging markets.

Funding Statement

This study was sponsored by GlaxoSmithKline Biologicals SA (Study identifier eTrack VEO000738). Support for third-party writing assistance for this article, provided by Costello Medical, UK was funded by GSK in accordance with Good Publication Practice (GPP) 2022 guidelines (https://www.ismpp.org/gpp-2022).

Authors’ contributions

Substantial contributions to study conception and design: NA, ER, VS, LT, JAG; substantial contributions to analysis and interpretation of the data: NA, ER, VS, LT, JAG; drafting the article or revising it critically for important intellectual content: NA, ER, VS, LT, JAG; final approval of the version of the article to be published: NA, ER, VS, LT, JAG.

Disclosure statement

NA: employed by GSK and holds financial equities in GSK; ER and VS: employed by GSK; LT: employed by GSK and shareholder of Sanofi; JG: previously employed by GSK and previously held financial equities in GSK.

Data availability statement

All data generated or analyzed during this study are included in this published article/as supplementary information files.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/21645515.2025.2507885