In the field of pharmacovigilance, vaccines represent an area where safety monitoring plays a particularly important role. Because vaccines are administered to millions of people, often within a short period and frequently to healthy individuals, continuous monitoring of adverse events is essential even after a vaccine has been authorized.
For this reason, pharmacovigilance and vaccines are closely linked. Through the collection, assessment, and analysis of reports of suspected adverse reactions, health authorities can identify potential safety signals and verify that the benefit-risk balance remains favorable over time.
How Pharmacovigilance and adverse event reporting work
Vaccine pharmacovigilance relies on structured systems for collecting and analyzing safety reports. In Italy, suspected adverse reactions are collected through the National Pharmacovigilance Network. These reports may subsequently contribute to European monitoring systems, including EudraVigilance, the European Medicines Agency’s database for suspected adverse reactions to medicines authorized or under investigation within the European Economic Area (EEA).
Reporting represents the first step in the pharmacovigilance process and is essential for gathering data that support safety evaluations. Under European regulations, healthcare professionals and members of the public can report any suspected adverse reaction, whether serious or non-serious, known or previously unrecognized, that occurs after vaccination.
Each report includes relevant information such as the description of the event, the time of onset, characteristics of the vaccinated individual, the vaccine administered, the batch number when available, and the outcome of the event. Subsequently, these data are assessed alongside other reports and additional scientific evidence.
Importantly, submitting a report does not require proof of a causal relationship. An event can be reported simply because it occurred after vaccination. In other words, a temporal association is sufficient to trigger data collection, while establishing a causal link requires further investigation.
As a result, pharmacovigilance systems can distinguish, through aggregated data and epidemiological assessments, between coincidental events and reactions that may be associated with a vaccine.
The specific characteristics of vaccines compared with other medicines
Although the core principles of pharmacovigilance apply to all medicinal products, vaccines have unique characteristics that require particular attention.
First, vaccines are commonly administered to healthy individuals and, in many cases, to very large populations. Consequently, the acceptable level of risk is particularly low, making it important to monitor even rare adverse events.
Moreover, vaccination campaigns may involve large numbers of people within a relatively short timeframe. This can lead to an increase in adverse event reports, including events that naturally occur within the general population. Therefore, safety experts must quickly differentiate between expected reactions, such as fever or injection-site pain, coincidental events, and potential safety concerns.
Another important factor is the high level of public interest surrounding vaccine safety. Because vaccines are a highly visible public health topic, effective monitoring systems and transparent communication are essential for maintaining public confidence.
How safety data are analyzed and safety signals identified
Once reports have been collected, specialists analyze the data to identify possible patterns, trends, or anomalies.
This process, known as signal detection, involves identifying information that suggests a potential new association—or a new aspect of a known association—between a vaccine and an adverse event. However, a safety signal does not automatically demonstrate that the vaccine caused the event. Instead, it indicates the need for further investigation.
When a potential signal emerges, more detailed evaluations are carried out. These assessments may include clinical reviews of individual cases, comparisons with the expected frequency of the event in the general population, reviews of scientific literature, and, when available, epidemiological studies or active surveillance data.
Only after these investigations have been completed can experts determine whether sufficient evidence exists to establish a vaccine-related risk. If necessary, regulatory authorities may update safety information, introduce specific recommendations, restrict certain uses, or implement other risk management measures.
Conclusion
Vaccine pharmacovigilance is a continuous and structured process designed to monitor vaccine safety throughout the entire product lifecycle, including the period after market authorization.
Through the systematic collection of adverse event reports and the ongoing analysis of safety data, health authorities can rapidly identify potential concerns and distinguish between coincidental events and genuine safety signals.
In this context, reporting suspected adverse reactions plays a crucial role. Every report contributes to a more comprehensive safety database and helps improve scientific understanding of a vaccine’s safety profile.
Ultimately, this approach supports a high level of public health protection while helping to maintain confidence in vaccination programs.
Sources
- Italian Medicines Agency (AIFA), How to Report an Adverse Reaction.
- European Medicines Agency (EMA), EudraVigilance and Signal Management.
- EudraVigilance, European Database of Suspected Adverse Drug Reaction Reports.
- World Health Organization (WHO), Global Manual on Surveillance of Adverse Events Following Immunization.