Safety and effectiveness of dose-sparing strategies for seasonal influenza vaccine
Authors: Antony Jesmin , Rios Patricia , Williams Chantal , Ramkissoon Naveeta , Straus Sharon E. , Tricco Andrea C. 
Published: August 2020

ABSTRACTBackgroundThe objective of this rapid scoping review was to identify potentially safe and effective dose-sparing strategies for intramuscular administration of seasonal influenza vaccines in healthy individuals of all ages.MethodsComprehensive literature searches were developed and executed in MEDLINE, EMBASE, and the Cochrane library, and grey literature was searched via international clinical trial registries for relevant studies published in English in the last 20 years. References of relevant systematic reviews and included studies were also scanned. Title/abstract and full-text screening were carried out by pairs of reviewers independently and data charting conducted by a single reviewer and verified by a second reviewer. Results were presented narratively.ResultsA total of 13 studies with 10,351 participants were included in the review and all studies were randomized control trials conducted between 2006 and 2019. The most common interventions were the trivalent influenza vaccine (n=10), followed by quadrivalent influenza vaccine (n=4). Nine studies included infants/toddlers 6-36 months old and one of these studies also included children and adolescents. In these nine studies, no clinical effectiveness outcomes were reported and no difference was found in local and systemic reactogenicity between dosing strategies. Of the four adult studies (≥ 18 years), the two studies that reported on effectiveness outcomes found similar results between the half-dose and full-dose vaccination groups and all four studies reported no differences in safety outcomes between groups.ConclusionThe current evidence for the administration of intramuscular influenza vaccines suggests there is no significant difference in safety and clinical effectiveness with the use of low-dose compared to full-dose vaccines, which is promising given the predicted resource constraints in the upcoming influenza season due to the 2019 novel coronavirus. Due to the low number of studies in adults and the lack of studies assessing confirmed influenza and influenza-like illness, there remains a need for further evaluation.EXECUTIVE SUMMARYPURPOSEThe Centre for Immunization and Respiratory Infectious Diseases of the Public Health Agency of Canada (PHAC) submitted a query regarding the safety and effectiveness of fractional dosing of seasonal influenza vaccines through the Canadian Institutes of Health Research (CIHR) Drug Safety and Effectiveness Network (DSEN). They requested that the DSEN Methods and Application Group in Indirect Comparisons (MAGIC) conduct a rapid review on this topic with an approximate 6-week timeline.The overall objective of this rapid review was to identify potentially safe and effective dose-sparing strategies for administration of seasonal influenza vaccines in healthy individuals of all ages that have been evaluated in human trials. In order to limit the scope of the work and ensure the rapid timeline could be met, this review focused only on intramuscular vaccine formulations, thus the research question was as follows:What is the safety and effectiveness of using fractional dosing strategies to deliver intramuscular seasonal influenza vaccines?