Harmonizing the collection of solicited adverse events in prophylactic vaccine clinical trials

During the clinical development of a vaccine, study participants are monitored for the occurrence of adverse events (AEs) over a defined period post-vaccination to assess the safety of prophylactic vaccines. Among the safety data collected, a standard practice in prophylactic vaccine clinical trials involves collecting reactogenicity data through daily AE solicitation of pre-defined sets of symptoms (i.e. solicited AEs).

This paper aims to propose recommendations to improve and harmonize the collection of active AE solicitation in prophylactic vaccine clinical trials.

We recommend using limited lists of solicited AEs adapted to the vaccine technology and target population. While the US Food and Drug Administration toxicity grading scale is commonly used in adolescents/adults, harmonizing grading criteria in infants/children would facilitate the comparison of vaccines' safety profiles. Solicited systemic AEs should not systematically be considered causally related to vaccination. Collection of solicited AEs should occur in cohorts of a maximum of 1,000 vaccinated participants, as larger cohort sizes do not improve substantially the precision of AE incidence. The incidence of daily solicited AEs should be compared with a control group for improved interpretations of their clinical relevance. These suggestions would improve the characterization of safety profiles of vaccines.