Demonstration of background rates of three conditions of interest for vaccine safety surveillance

Abstract

IntroductionAdverse events following immunization (AEFIs) are unwanted or unexpected health outcomes following vaccination, which may or may not be causally-linked to vaccines. AEFI reporting is important to post-marketing vaccine safety surveillance and has the potential to identify new or rare AEFIs, show increases in known AEFIs, and help to maintain public confidence in vaccine programs. Knowledge of the expected incidence (i.e. background rate) of a possible AEFI is essential to the investigation of vaccine safety signals. We selected three rarely reported AEFIs representing the spectrum of causal association with vaccines, from proven (immune thrombocytopenia [ITP]) to questioned (Kawasaki disease [KD]) to unsubstantiated (multiple sclerosis [MS]) and determined their background rates.MethodsWe extracted data on hospitalizations (CIHI Discharge Abstract Database) for ITP, KD, and MS among Ontario children for the period 2005 to 2014 from IntelliHEALTH. As ITP can be managed without hospitalization, we also extracted emergency department (ED) visits from the CIHI National Ambulatory Care Reporting System. For all conditions, we only counted the first visit and if the same child had both an ED visit and a hospitalization for ITP, only the hospitalization was included. We calculated rates by year, age group and sex using population estimates from 2005–2014, focusing on age groups within the Ontario immunization schedule around vaccine(s) of interest.ResultsPer 100,000 population, annual age-specific incidence of ITP in children age 1 to 7 years ranged from 8.9 to 12.2 and annual incidence of KD in children less than 5 years ranged from 19.1 to 32.1. Average annualized incidence of adolescent (11–17 years) MS across the study period was 0.8 per 100,000.DiscussionDespite limitations, including lack of clinical validation, this study provides an example of how health administrative data can be used to determine background rates which may assist with interpretation of passive vaccine safety surveillance.

Background incidence rates of adverse events of special interest related to COVID-19 vaccines in Ontario, Canada, 2015 to 2020, to inform COVID-19 vaccine safety surveillance

“…Our estimated background rates of Kawasaki disease are within the previously reported range of 19.1–32.1 per 100,000 in Canadian children younger than 5 years of age [39] and 5.1–50.4 per 100,000 in US children aged 0–6 years of age. [36] Similar to those studies, we also observed higher rates for males than females among children aged 0–4 years.…”

“…Imperfect validity of the diagnostic codes in administrative data without information on clinical and/or diagnostic confirmation may have resulted in under or overestimation. However, we used previously validated codes and/or codes that have been used in previous studies [32] , [39] , [40] to improve the accuracy of case ascertainment in administrative data. The quality of DAD hospitalization data has been previously evaluated.…”

“…Where available, we used codes that have been validated and/or used in previous studies. [32] , [39] , [40] Hospitalizations and emergency department visits were identified from the Canadian Institute for Health Information (CIHI) Discharge Abstract Database (DAD) and CIHI’s National Ambulatory Care Reporting System, respectively. For hospitalizations, we included cases where an ICD-10-CA code of interest was listed as the final diagnosis at discharge, was present on admission and of primary relevance to the stay, and was not listed as a secondary diagnosis, comorbidity, or as part of the medical history.…”

Background incidence rates of adverse events of special interest related to COVID-19 vaccines in Ontario, Canada, 2015 to 2020, to inform COVID-19 vaccine safety surveillance

“…Our estimated background rates of Kawasaki disease are within the previously reported range of 19.1-32.1 per 100,000 in Canadian children younger than 5 years of age 32 and 5.1-50.4 per 100,000 in US children aged 0-6 years of age. 40 Similar to those studies, we also observed higher rates for males than females among children aged 0-4 years.…”

Adverse events following pediatric immunization in an Indian city

“…A major public health concern regarding vaccines relates to their safety and the risks of AEs occurring at or after vaccination [ 8 9 ]. Since vaccines are mainly administered to healthy and young people, even non-serious AEs are often deemed unacceptable by vaccinees or their parents/relatives.…”