From 1980 to 2023: A Long-Term Observation of Third-Dose Hepatitis B Vaccine Coverage and Global Public Health Delivery Capacity

An Often Underestimated Indicator

Hepatitis B vaccine third dose (HepB3) coverage has long appeared in the annual immunization estimates of the World Health Organization and UNICEF (the WUENIC system), but it is usually cited as a technical health indicator rather than a capacity indicator.

This understanding underestimates its information content. HepB3 measures not the peak that a vaccination campaign can achieve, but whether a system can deliver three doses on time, by dose, and across populations to nearly all newborns within the first year after birth through routine services rather than emergency mobilization. To do this, the cold chain must remain unbroken, electricity must be available, vaccination points must be within walking distance or short-distance transport, primary health workers must complete follow-up, and registration and reporting systems must aggregate scattered vaccination records into verifiable data.

In other words, HepB3 is a delivery-capacity curve compressed into a single number.

1980–2023: What Forty-Three Years Covered

If the observation window is extended to 1980, the starting point is nearly blank. Universal infant hepatitis B immunization programs did not yet exist globally at that time; in 1992, WHO recommended incorporating hepatitis B vaccine into national immunization programs, followed by a multi-layered introduction process lasting more than thirty years.

These forty-three years also accommodated several parallel lines of change:

• Technology line: vaccines shifted from plasma-derived to recombinant technology, and the boundaries of supply scale and safety changed accordingly;
• Platform line: the spread of pentavalent vaccine (DTP-HepB-Hib) changed delivery models, embedding hepatitis B vaccine into the existing DTP delivery chain and significantly reducing marginal delivery costs;
• Financing line: mechanisms represented by Gavi, the Vaccine Alliance, covered procurement costs during the introduction phase and part of the system-building costs in low-income countries;
• Data line: monitoring gradually shifted from countries' paper annual reports to a standardized, annualized international estimation system.

These four lines did not advance in sync. Technological availability often preceded financing arrangements, and financing arrangements preceded data visibility. Therefore, a long-term coverage curve is actually the result of multiple institutional variables superimposed, not a readout of the effect of a single policy.

The Spatial Dimension Is Harder to Handle Than the Temporal Dimension

The 204 countries and territories are not homogeneous units. National averages can mask differentiation within provinces, states, districts, and even cities: a system whose national average coverage has already reached target may still have structurally low-coverage areas in certain provinces, border zones, or rapidly expanding urban fringes.

The methodological significance of spatiotemporal analysis lies precisely in handling temporal trends and spatial dependence simultaneously. Spatial autocorrelation tests are used to determine whether neighboring units tend to show similar coverage rates; hotspot and coldspot identification is used to locate persistent low-coverage areas rather than single-year low values; and hierarchical structures are used to distinguish "national effects" from "local effects."This distinction is highly practical for decision-making. If low coverage is mainly caused by national-level procurement or fiscal constraints, the solution lies at the central level; if low coverage is concentrated in a few areas and stable over the long term, the problem is more likely to lie in local health workforce, transportation accessibility, or service organization. The intervention paths for the two types of problems are completely different, and national annual reports cannot separate the two.

Vaccines Are an Extremely Demanding Form of Infrastructure

From the perspective of infrastructure studies, immunization programs are not fundamentally different from energy and transportation networks; they are simply subject to tighter constraints.

Hepatitis B vaccine must be kept in the cold chain throughout at 2–8°C; the birth dose is recommended to be given within 24 hours of birth. These two requirements directly tie vaccine delivery to three types of hardware systems:

First, electricity and refrigeration. In areas with unstable grids, the cold chain often relies on solar direct-drive refrigeration equipment, directly coupling immunization programs with distributed energy investment.

Second, roads and passability. Fixed vaccination sites have a limited coverage radius, and the cost of outreach vaccination is almost entirely determined by road conditions. Road segments impassable during the rainy season directly manifest as seasonal dips in coverage curves.

Third, data and registration. Tracking “zero-dose children” presupposes knowing who they are and where they were born. The completeness of the birth registration system therefore becomes an implicit ceiling on immunization coverage.

Procurement and Financing Structure

Global procurement of hepatitis B vaccine is highly concentrated among a few international suppliers and is mainly priced through long-term agreements and pooled procurement mechanisms of the UNICEF Supply Division. This structure has brought significant price reductions, but it also means that supply concentration itself constitutes a risk point.

On the demand side, however, the divergence of financing sources is more critical: in some low-income countries, introduction costs are borne by international mechanisms; as country income classifications change, procurement responsibility gradually shifts to domestic financing. This “transition” phase is often the most fragile segment of coverage curves—there is a time lag between the withdrawal of international support and the continuation of domestic budgets, and immunization programs have no inventory buffer.

External Shocks and System Resilience

The COVID-19 pandemic provided the clearest stress test in recent years. Annual estimates from WHO and UNICEF show that in 2021, about 25 million children worldwide did not receive diphtheria-tetanus-pertussis-containing vaccines through routine immunization services, one of the worst levels since the 2000s. The third dose of hepatitis B vaccine, as an indicator on the same delivery chain, likewise showed a corresponding deviation in its coverage trajectory.

It is worth noting that what the shock exposed was not procurement capacity but delivery redundancy. The vaccine may already be in the warehouse; the problem is whether it can be delivered to people. This again shows that the key variable for assessing an immunization system lies at the local level, not in the central warehouse.

The 2030 Target and That Most Stable Structural FactWHO, in its global health sector strategy on viral hepatitis, set 2030 as the target year for eliminating viral hepatitis as a public health threat. Related targets include infant hepatitis B vaccine third-dose coverage reaching the 90% level, and reducing hepatitis B surface antigen prevalence among children under 5 to an extremely low level.

Within this entire set of targets, one structural fact has remained stable over the long term: birth-dose coverage is consistently lower than third-dose coverage globally.

The reason is not mysterious. The third dose can piggyback on the existing DTP delivery chain and be completed through a mature infant follow-up schedule; the birth dose, by contrast, requires intervention in the delivery room or within a very short time window after birth, touching the systemic interface between obstetric services and immunization programs.

This is not a funding problem but an organizational one: it requires four systems—obstetric records, birth registration, cold chain supply, and immunization follow-up—to coordinate within the same time window. If any link falls out of sync, birth doses are lost. Therefore, the rate of improvement in birth-dose coverage often reflects the degree of integration of a health system better than the third dose does.

Long-term implications

204 countries and territories, forty-three years, one indicator.

The spatiotemporal distribution of vaccine coverage is essentially a long-term projection of a country's public service delivery capacity. It is highly correlated with electricity coverage, road accessibility, density of primary health workforce, and fiscal transfer payment capacity. For infrastructure and regional development researchers, such data provide a continuous series for observing the evolution of state capacity—it is more stable than any single-year investment announcement, and harder to be embellished by short-term narratives.

This is also the true value of spatiotemporal analysis relative to single-year snapshots: it shifts attention from "how much was achieved in a given year" to "under what conditions it can be sustained."

For the study's specific estimates, regional heterogeneity results, and statistical details, please refer to the original text.