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WOAH Biological Standards Commission decides to relaunch a global call for new tuberculin candidates after extensive international trials
Following a decade of international studies, the WOAH Biological Standards Commission, supported by an ad hoc group of experts, has concluded that the proposed replacement candidates for the International Standard for Bovine Tuberculin do not meet the required potency levels. It will now relaunch a global call for new candidates’ materials.
What is the International Standard for Bovine Tuberculin?
The International Standard Bovine Tuberculin (ISBT) is a biological reference material derived from Mycobacterium bovis strain AN5. Established nearly three decades ago, it defines a standardised protein concentration that serves as the global benchmark for tuberculin potency testing.
ISBT is used worldwide in bovine tuberculosis control programmes for screening cattle. All commercial bovine tuberculin preparations must be calibrated against this standard.
The science behind tuberculin testing
Tuberculin testing exploits the immune system’s memory of infection. When Mycobacterium tuberculosis complex organisms infect cattle, the animal’s immune system develops a hypersensitivity response to specific bacterial proteins. The tuberculin skin test capitalises on this biological activity by injecting purified protein derivative (PPD) intradermally and measuring the resulting immune response as an increase in skin thickness. This delayed hypersensitivity reaction, measured 72 hours post-injection, indicates prior exposure to tuberculosis.
A decade-long effort to replace the standard
The current ISBT, established in 1986, has been in limited supply since 2015. In response, WOAH’s Biological Standards Commission, supported by an ad hoc group of mammalian tuberculosis reference laboratory experts, has coordinated experiments with multiple laboratories, research institutes and tuberculin manufacturers across continents to identify a suitable replacement.
Key findings
Two candidates were initially shortlisted in 2017. Following further evaluation, only one (Candidate B) progressed to international collaborative trials conducted between 2018 and 2025.
However, the latest assays revealed persistent potency shortfalls:
- Potency levels (18,000–19,116 IU/mg) remained well below the required minimum of 32,000 IU/mg.
- Multiple laboratories confirmed inconsistent results despite protocol refinements.
- High assay variability and weak dose-response relationships hindered reliable potency determination.
Final trials in November 2025 confirmed that Candidate B does not meet the criteria to replace ISBT.
Future directions
The Biological Standards Commission acknowledged that PPD is a complex biological substance having many specific and non-specific proteins. They emphasised that accepting a lower potency international standard would compromise the comparability of global tuberculin standardisation across laboratories and batches.
The Commission therefore decided to:
- relaunch a global call for new tuberculin candidates.
- support the development of alternative approaches for PPD-based tests such as the Molecularly Defined Tuberculins (MDTs) which use specific peptides as a long-term alternative to traditional PPD-based assays.
While promising, MDTs require further field validation across different epidemiological settings before they can replace current methods.
More information
The full meeting report, including detailed methodology and statistical analyses, is available on the WOAH website:
WOAH Ad hoc Group on Replacement of the International Standard for Bovine Tuberculin. Report 2015-2025.
Ad hoc Groups – WOAH – World Organisation for Animal Health
Biological Standards Commission – WOAH – World Organisation for Animal Health
Contact: [email protected]
Field evaluation and post-vaccination monitoring for informed decision-making
The right evidence, at the right moment, can guide better decisions.
As African swine fever (ASF) continues to affect pig production, animal health systems and safe trade worldwide, WOAH has published new guidelines to support evidence-based vaccine use. The Guidelines for African swine fever vaccines: field evaluation and post-vaccination monitoring provide practical guidance to help Members implement international standards and mitigate risks associated with substandard vaccines.
Developed with experts from The Pirbright Institute and the Centre for Applied One Health Research and Policy Advice at City University of Hong Kong, the guidelines are now available and provide a practical, field-oriented reference for Veterinary Services, competent authorities and other stakeholders involved in vaccine deployment.
Supporting evidence-based decisions in the field
ASF vaccination is rapidly evolving. While vaccine candidates are under development and some live attenuated virus vaccines have received regulatory approval in certain countries, WOAH emphasises that only high-quality vaccines manufactured according to international standards should be used. Vaccination decisions must be grounded in reliable evidence and adapted to local epidemiological conditions. The guidelines support Members in generating and assessing this evidence, covering the design, implementation and evaluation of field studies, as well as the benefit–risk assessment that should precede any national or regional vaccination programme. Practical tools, including sample size calculators and recording form templates, are included to help users apply the guidance directly on the ground.
From field trials to post-vaccination monitoring
Running a field trial well requires getting many things right at once: clear case definitions, appropriate study designs, rigorous randomisation, consistent data collection and validated laboratory testing. The guidelines walk users through each of these elements, with worked examples where possible, to ensure that field evaluations generate evidence that is both reliable and usable for decision-making.
Post-vaccination monitoring is equally important. The guidelines cover the systematic tracking of vaccine effectiveness under real-world conditions, alongside pharmacovigilance to detect side effects or adverse events. A dedicated three-step framework is provided to help countries set up and sustain monitoring systems, from establishing expected side effects and reporting channels to periodically evaluating and revising the programme. Genomic surveillance, including whole genome sequencing where feasible, is also recommended to detect potential reversion to virulence or recombination events over time.
Vaccination as one tool among many
These guidelines make clear that vaccination is not a standalone solution. It must be integrated into comprehensive ASF prevention and control strategies, alongside biosecurity, surveillance and movement controls, tailored to each Member.
Bringing technical guidance closer to Members
Aligned with WOAH’s commitment to supporting Members in building robust animal health systems, the guidelines are designed to be adapted rather than applied rigidly. Countries with sufficient resources are encouraged to conduct their own field trials. Others can draw on data from countries with comparable production systems, with WOAH facilitating connections to relevant Reference Laboratories and Collaborating Centres. Transparency and data sharing are highlighted throughout, in keeping with the principles of the Terrestrial Animal Health Code.
ASF is a transboundary disease, what happens in one country affects its neighbours. That is why the evidence generated through field trials needs to be shared, not kept in silos.
Upcoming webinar
To support the practical use of these guidelines, WOAH will host a webinar on 30 June 2026, bringing together the authors and selected Members to discuss the application of this resource.
More information
Guidelines for African swine fever vaccines: field evaluation and post-vaccination monitoring
Contact: [email protected]