As African swine fever vaccines move from laboratory promise to field deployment, a critical question has gone largely unanswered: how should countries rigorously evaluate whether those vaccines actually work under real-world conditions? The World Organisation for Animal Health (WOAH) has now published comprehensive guidelines designed to answer exactly that.
Released on June 25, 2026, the Guidelines for African Swine Fever (ASF) Vaccines: Field Evaluation and Post-Vaccination Monitoring offer a technical framework developed in collaboration 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 intended for Veterinary Services, biosecurity authorities, and other stakeholders involved in vaccine deployment decisions.
The timing is significant. African swine fever virus (ASFV) — a transboundary pathogen that affects both domestic and wild pigs — has spread over the past decade from its origins in sub-Saharan Africa to countries across Asia, Europe, and most recently the Caribbean island of Hispaniola. The disease has caused devastating losses to global pig production and food security. Until recently, no effective vaccine existed. That has begun to change: commercially produced live attenuated virus (LAV) vaccines have received regulatory approval in several Southeast Asian countries, including Vietnam and the Philippines, and are now in active use. Other countries are weighing whether to follow.
Rigorous Field Trials Before Deployment: The Core Recommendation
The guidelines’ central message is unambiguous: countries should not authorize or deploy a new ASF vaccine without first conducting field trials to assess its real-world performance. While vaccine manufacturers typically provide efficacy data from controlled laboratory studies, WOAH emphasizes that performance can vary significantly across different production systems, pig breeds, biosecurity levels, and circulating virus strains. Field evaluations fill that gap.
The document’s key recommendations include:
- Base deployment decisions on a clear national objective, whether that is reducing outbreaks, lowering mortality, limiting transmission, or supporting recovery of disease-free status and trade access.
- Conduct randomized controlled trials (RCTs) in the field before launching any national or regional vaccination programme. RCTs are described as the gold standard for vaccine efficacy evaluation and can be designed at the individual pig level, the pen or farm level (cluster randomization), or through stratified or stepped-wedge designs depending on resources and objectives.
- Establish a post-vaccination monitoring and pharmacovigilance system before rollout to detect side effects, adverse events, and changes in vaccine performance.
- Integrate genomic surveillance, including whole genome sequencing where feasible, to detect potential reversion to virulence or recombination events — two major concerns specific to live attenuated virus vaccines.
- Ensure independent oversight: field trials and monitoring programmes should be overseen by an advisory committee with no conflict of interest in vaccine production, distribution, or rollout.
From Case Definitions to Clinical Scoring: What the Guidelines Actually Provide
The guidelines also offer practical tools for implementation. They walk users through how to define ASF cases in a vaccinated population — a non-trivial challenge, since vaccine-related viral shedding and post-vaccination side effects can complicate interpretation of laboratory and clinical findings. A detailed clinical scoring system for individual pigs is provided, rating signs such as liveliness, posture, skin discoloration, respiratory status, and neurological function on a scale that can trigger case investigation when a threshold is exceeded.
Outcome measures for vaccine efficacy studies should be linked to the vaccination programme’s objectives and local ASF control goals, which may differ between an endemic region seeking to reduce mortality and a previously disease-free region seeking to maintain or regain that status. The guidelines illustrate this with worked scenario examples and a table mapping programme goals to appropriate outcome measures.
For study design, the document provides detailed guidance on randomization procedures, sample size calculation, inclusion and exclusion criteria, blinding protocols, vaccination and sampling schedules, and validated laboratory testing methods. Sample size calculators and standardized recording form templates are included as ready-to-use annexes.
Post-vaccination monitoring is addressed through a dedicated three-step pharmacovigilance framework: first, establish a list of expected side effects based on manufacturer data and field reports from other countries; second, develop an action plan, communication protocols, and a reporting database; and third, periodically evaluate and revise the programme. Common side effects to watch for with LAV vaccines include lethargy, temporary fever, weight loss, and disease in immunodeficient animals.
Vaccination as One Tool Among Many — and the Imperative to Share Data
Throughout the document, WOAH is careful to frame vaccination not as a standalone solution but as one component of a comprehensive ASF prevention and control strategy that must also include biosecurity, movement controls, and surveillance. Countries are advised to conduct a benefit–risk assessment before launching a national programme, and to revisit that assessment once post-vaccination monitoring data are available.
The guidelines also place strong emphasis on data sharing. Because ASF is a transboundary disease, evidence generated in one country has direct value for its neighbors. Countries with sufficient resources are encouraged to conduct their own field trials; those with limited capacity are encouraged to draw on data from countries with comparable production systems, with WOAH facilitating connections to relevant Reference Laboratories and Collaborating Centres. Public–private partnerships are encouraged to facilitate transparency, including through publication of summary reports where full data disclosure is constrained by commercial confidentiality.
ASF has already disrupted pig production systems on multiple continents and threatens food security in countries where pork is a dietary staple. The introduction of vaccines has raised hopes for more effective control, but also new risks — particularly around the potential for live attenuated vaccine strains to revert to virulence or recombine with circulating wild-type strains. Standardized, evidence-based approaches to field evaluation and ongoing monitoring are essential to ensure that vaccination programmes deliver their intended benefits without introducing new hazards.
WOAH will host a webinar on June 30, 2026, featuring the guidelines’ authors and selected member country representatives to support practical application of the new resource.
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