Safety monitoring in the Vaccine Adverse Event Reporting System (VAERS)

Abstract

The Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) conduct post-licensure vaccine safety monitoring using the Vaccine Adverse Event Reporting System (VAERS), a spontaneous (or passive) reporting system. This means that after a vaccine is approved, CDC and FDA continue to monitor safety while it is distributed in the marketplace for use by collecting and analyzing spontaneous reports of adverse events that occur in persons following vaccination. Various methods and statistical techniques are used to analyze VAERS data, which CDC and FDA use to guide further safety evaluations and inform decisions around vaccine recommendations and regulatory action. VAERS data must be interpreted with caution due to the inherent limitations of passive surveillance. VAERS is primarily a safety signal detection and hypothesis generating system. Generally, VAERS data cannot be used to determine if a vaccine caused an adverse event. VAERS data interpreted alone or out of context can lead to erroneous conclusions about cause and effect as well as the risk of adverse events occurring following vaccination. CDC makes VAERS data available to the public and readily accessible online. We describe fundamental vaccine safety concepts, provide an overview of VAERS for healthcare professionals who provide vaccinations and might want to report or better understand a vaccine adverse event, and explain how CDC and FDA analyze VAERS data. We also describe strengths and limitations, and address common misconceptions about VAERS. Information in this review will be helpful for healthcare professionals counseling patients, parents, and others on vaccine safety and benefit-risk balance of vaccination.

Keywords: Adverse effect; Adverse event following immunization; Adverse reaction; Passive surveillance; Spontaneous reporting; Vaccination; Vaccine Adverse Event Reporting System (VAERS); Vaccine adverse event; Vaccine safety.

Figure 1. Adverse event following immunization (AEFI) and the VAERS reporting timeline

^*“Adverse event following immunization” (AEFI) indicates only that the event happened after vaccination (i.e., a temporal association). ^†“Vaccine adverse reaction” and “vaccination adverse effect” are also AEFIs, but imply that the vaccine caused the event (i.e., a causal association). ^¶There are no deadlines or time limits for the submission of a VAERS report, but reports should be submitted promptly after an adverse event occurs to facilitate surveillance and review. The National Vaccine Injury Compensation Program (VICP) is administered by the Health Resources and Services Administration (HRSA). The VICP is separate from the VAERS program and reporting an adverse event to VAERS does not constitute filing a claim for compensation to the VICP (see www.hrsa.gov/vaccinecompensation/index.html).

Figure 2. Vaccine Adverse Event Reporting System (VAERS) report submission^* and data flow

^*During the time period 2011-2014, healthcare professionals submitted 38% of U.S. reports, patients and parents submitted 14%, vaccine manufacturers submitted 30%, and others (e.g., friends/acquaintances of the patient, 3^rd party reporters who became aware of adverse events from the media, lawyers, etc.) submitted 12% (CDC unpublished data). There is variability in reporter type across different types and brands of vaccines. ^†Wide-ranging Online Data for Epidemiologic Research ^¶Medical Dictionary for Regulatory Activities

Figure 3

2×2 contingency table illustrating a hypothetical single vaccine and adverse event (AE) combination scenario