Vaccines are among the most effective public health interventions, preventing millions of deaths each year. However, because vaccines are administered to large and often healthy populations, their safety is subject to intense scrutiny. Vaccine safety surveillance and pharmacovigilance systems are designed to detect, assess, and communicate risks in a transparent manner, thereby maintaining public confidence in immunization programmes. Alongside surveillance, effective communication plays a decisive role, especially during drug safety crises.

Vaccine Pharmacovigilance: A Specialized Discipline

Vaccine pharmacovigilance refers to the science and activities dedicated to the detection, assessment, understanding, and prevention of adverse events related to vaccines. Unlike conventional drugs, vaccines are often given to healthy individuals, including infants and children, making safety expectations exceptionally high. Vaccine pharmacovigilance therefore focuses not only on adverse reactions but also on programmatic errors, cold-chain issues, and immunization practices.

Global vaccine safety activities are coordinated through international collaboration, particularly under the guidance of the World Health Organization (WHO), which supports member states in strengthening vaccine safety systems.

Vaccination Failure: Understanding Reduced Effectiveness

Vaccination failure occurs when an individual does not develop adequate immunity despite receiving a vaccine. This may result from primary failure, where immunity is never achieved, or secondary failure, where immunity wanes over time. Factors such as improper storage, incorrect administration, host immune status, or pathogen variation can contribute to vaccination failure.

Monitoring vaccination failures is an important component of vaccine pharmacovigilance, as it helps identify issues related to vaccine quality, handling, or immunization schedules.

Adverse Events Following Immunization (AEFI)

Adverse Events Following Immunization (AEFI) are any untoward medical occurrences that follow vaccination and do not necessarily have a causal relationship with the vaccine. AEFIs may range from mild reactions such as fever and pain at the injection site to rare but serious events like anaphylaxis.

AEFI surveillance systems aim to distinguish coincidental events from vaccine-related reactions through systematic investigation and causality assessment. Transparent reporting and analysis of AEFIs are essential to maintaining public trust in vaccination programmes.

Pharmacovigilance Methods

Passive Surveillance: Foundation of Safety Monitoring

Passive surveillance relies on spontaneous reporting of adverse events by healthcare professionals, manufacturers, and sometimes patients. This includes individual case safety reports and case series submitted to national or international databases. Passive systems are cost-effective and wide-reaching but are often limited by under-reporting and variable data quality.

Stimulated Reporting: Enhancing Awareness

Stimulated reporting is used to increase reporting rates during specific situations, such as the introduction of a new vaccine or during mass immunization campaigns. Educational initiatives, reminders, and simplified reporting tools encourage healthcare professionals to report adverse events more actively, improving early signal detection.

Active Surveillance: Proactive Safety Monitoring

In contrast to passive systems, active surveillance proactively seeks information on adverse events. Methods include sentinel sites, where selected healthcare facilities actively monitor vaccine recipients, and drug event monitoring systems that follow patients over time.

Registries, such as pregnancy or disease-specific registries, provide structured data on defined populations, enabling more accurate estimation of adverse event rates and risk factors.

Comparative Observational Studies

Comparative observational studies play a crucial role in evaluating associations between vaccines and adverse events. Cross-sectional studies assess exposure and outcomes at a single point in time, while case–control studies compare individuals with a specific adverse event to those without it. Cohort studies follow exposed and unexposed populations over time to estimate risk.

These methods are particularly valuable for assessing rare or delayed adverse events that cannot be easily studied in clinical trials.

Targeted Clinical Investigations

When safety signals emerge, targeted clinical investigations may be conducted to explore causality in greater depth. These studies are designed to answer specific safety questions and often involve focused clinical evaluation, laboratory testing, or mechanistic research.

Communication in Pharmacovigilance

Effective Communication as a Core Function

Effective communication is central to pharmacovigilance, ensuring that safety information is conveyed accurately, timely, and transparently. Clear communication helps healthcare professionals make informed decisions and reassures the public that risks are being actively managed.

Pharmacovigilance communication must balance scientific accuracy with clarity, avoiding unnecessary alarm while ensuring that important risks are not minimized.

Communication in Drug Safety Crisis Management

During a drug safety crisis, such as the detection of a serious vaccine-related adverse event, communication becomes even more critical. Crisis communication strategies focus on rapid information dissemination, consistent messaging, and proactive engagement with stakeholders.

Failure to communicate effectively during a crisis can erode public trust and undermine immunization programmes, even when risks are low.

Communicating with Key Stakeholders

Pharmacovigilance communication involves multiple stakeholders, including regulatory agencies, business partners, healthcare facilities, and the media. Regulators require detailed and timely safety reports to guide decision-making. Healthcare facilities need practical guidance to manage patient care, while business partners rely on clear communication to ensure compliance.

Engagement with the media and public should be transparent and evidence-based, helping to counter misinformation and promote confidence in vaccine safety systems.