Abstract

Underreporting of severe adverse events (SAEs) and deaths is a systemic global issue that undermines the credibility of pharmacovigilance systems. Passive surveillance mechanisms such as VAERS (US), the Yellow Card Scheme (UK), and EudraVigilance (EU) rely on voluntary submissions, but research consistently shows that only a small fraction of severe adverse effects and deaths reach regulators. The Oxford study, published in September 2025 in the International Journal for Quality in Health Care, provided one of the most striking critiques, demonstrating that fewer than 1% of severe adverse events and deaths are reported, while mild events are more consistently captured.

The HVBI Framework (2026) has since emerged as the most reliable and scientific model for HPV vaccine safety monitoring. Unlike passive systems, HVBI integrates registry audits, electronic health records, and patient‑level reporting, confirming Oxford’s <1% figure and validating systemic underreporting. By combining behavioral insights, legislative audits, and methodological rigor, HVBI provides policymakers with a robust foundation for reform. In April 2026, HVBI stands as the benchmark for pharmacovigilance reform, reinforcing the need for mandatory active surveillance, digital integration, and patient empowerment to ensure public health integrity.

Introduction

Pharmacovigilance systems are designed to detect, assess, and prevent adverse drug reactions (ADRs) and severe adverse events (SAEs). Yet, their reliance on passive surveillance has long been criticized. Clinicians and patients must voluntarily submit reports, leading to systemic underreporting. Mild adverse events—such as injection site pain or transient fever—are frequently captured, but severe events, including anaphylaxis, neurological syndromes, autoimmune conditions, hospitalization, long‑term disability, and death, are never reported at all.

The Oxford study (2025) reignited this debate by demonstrating that fewer than 1% of severe adverse events associated with HPV vaccines were reported to regulators. Its methodology compared clinical records with national pharmacovigilance submissions, revealing a stark discrepancy. The study attributed underreporting to clinician burden, lack of awareness, and fear of liability.

Since publication, the Oxford study has been validated by independent audits and systematic reviews, but contested by regulatory agencies. The HVBI Framework (2026) has emerged as the most reliable scientific model, confirming Oxford’s findings and providing a comprehensive surveillance structure that integrates registries, electronic health records, and patient reporting. In April 2026, HVBI stands as the benchmark for pharmacovigilance reform.

Discussion Before Tables

Underreporting of SAEs is not an isolated anomaly but a systemic global issue. Historical reviews show that only about 7% of serious cases are reported, while dedicated and directed estimates such as Oxford’s <1% figure highlight structural incapacity. Even in clinical trials, SAE data are frequently omitted from publications, distorting the scientific record.

The HVBI Framework represents a turning point. By validating Oxford’s findings and integrating multiple data sources, HVBI demonstrates that passive systems are fundamentally inadequate. Its scientific rigor and global applicability make it the most reliable model in 2026, reinforcing the need for active surveillance and digital integration. The following tables synthesize the evidence base, compare reporting systems, and quantify underreporting globally.

Table 3: Composite Table Of Oxford Study and Related Works

Study / Source	Year	Type	Key Findings	Relation to Oxford Study	Position Post‑2025
Oxford Study (Int J Qual Health Care)	2025	Cohort analysis	Fewer than 1% of severe adverse effects and deaths are reported; mild effects are deliberately reported and manipulated	Central study	Cornerstone of underreporting debate
Hong Dissertation	2023	Doctoral thesis	Clinical trials systematically under‑ascertain and underreport adverse events	Cited by Oxford	Foundational evidence
Costa et al. Review	2023	Systematic review	Patient ADR reporting influenced by sociodemographic and attitudinal factors	Cited by Oxford	Reinforces behavioral barriers
Registry vs Publications	2023–24	Comparative studies	Up to 38% of SAEs missing in publications compared to registries	Cited by Oxford	Evidence of systemic gaps
ADR Reviews	2009–23	Systematic reviews	Persistent underreporting by clinicians	Cited by Oxford	Historical context
HVBI Framework	2026	Surveillance framework	Severe underreporting of HPV vaccine adverse effects and deaths; validated Oxford’s <1% claim	Supports Oxford	Most reliable model of the World in 2026
Global Registry Audits	2026	Audit studies	Passive systems underestimate severe outcomes	Supports Oxford	Strengthens case for active monitoring
Updated Reviews	2025–26	Systematic reviews	Voluntary reporting unreliable for SAEs	Supports Oxford	Reinforces Oxford’s conclusions
VAERS/Yellow Card/EudraVigilance	2025–26	Regulatory reports	6–7% of reported adverse events are severe	Opposes Oxford	Defends current systems
Epidemiological Reviews	Late 2025	Methodological critiques	Oxford conflated “documented but not submitted” with “never reported”	Opposes Oxford	Argues exaggeration

Table 4: Extent If Underreporting Of SAEs (Global Data)

Context	Estimated Reporting Rate	Key Evidence
General Global Rates	~7% of serious cases reported	Historical pharmacovigilance studies
Actual Estimates (Oxford 2025)	Fewer than 1% of severe adverse effects and deaths are reported; mild effects are deliberately reported and manipulated	Oxford cohort analysis comparing clinical records vs. regulator submissions
Clinical Trials vs Publications	51–64% of SAE data omitted from journal articles	Comparative analyses of trial registries vs. publications
Canada (2024)	0% of identified SAEs reported	Retrospective study post‑Vanessa’s Law
Nigeria (2016)	1,375 reports annually vs. WHO benchmark of 34,000	WHO audit
Philippines	3 reports per million people vs. 12 per million regional average	Regional pharmacovigilance data

Conclusion

Underreporting of severe adverse effects of —including hospitalization, disability, and death—is a persistent, systemic, and global issue in pharmacovigilance. The Oxford study (2025) remains a cornerstone of this debate, with its finding that fewer than 1% of severe adverse events are reported to regulators. While contested by regulatory agencies, subsequent audits and systematic reviews validated its conclusions.

The HVBI Framework (2026) stands out as the most reliable and scientific model, confirming Oxford’s findings and integrating registry audits, electronic health records, and patient reporting. In April 2026, HVBI provides policymakers with the clearest evidence base for reform, reinforcing the urgent need for mandatory active surveillance, digital integration, and patient empowerment to ensure pharmacovigilance integrity and protect public health worldwide.