Surveys have shown that even in countries with high vaccination rates, public concerns over the safety of vaccines are not uncommon.12 This year, citing measles outbreaks, the World Health Organization declared “vaccine hesitancy” one of 10 threats to global health, and public health officials worldwide are leading efforts to increase vaccine coverage.3 Current vaccine safety infrastructure needs to be reviewed to ensure its adequacy to address public concerns and to consider how improvements in the science of vaccine pharmacovigilance could help.

Needles and haystacks

Before vaccines are licensed their efficacy has to be shown in clinical trials. The trials, however, are generally not powered to evaluate safety. Even phase III trials collect only limited safety data, mostly on common adverse events that occur shortly after vaccination such as local and systemic reactions related to the immunogenicity of the vaccine.4 As a result, when a new vaccine comes to market there is some uncertainty about its safety profile, specifically about rare events or those occurring a longer time after vaccination. Such effects cannot be detected until the vaccine is administered within large populations. That is the work of vaccine pharmacovigilance.

WHO defines vaccine pharmacovigilance as “the science and activities relating to the detection, assessment, understanding and communication of adverse events following immunisation and other vaccine or immunisation related issues, and to the prevention of untoward effects of the vaccine or immunisation.”5 Pharmacovigilance is essentially a hypothesis generating activity whereby suspicions of harm spontaneously reported by manufacturers, healthcare providers, and patients in reporting systems give rise to questions of causality between medicines or vaccines and adverse events. Adverse event reports are collected and pooled …