Safety and effectiveness of dose-sparing strategies for seasonal influenza vaccine: a rapid scoping review of fractional dosing of the intramuscular influenza vaccine

Antony, J.; Rios, P.; Williams, C.; Ramkissoon, N.; Straus, S. E.; Tricco, A. C.

Background: The 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. Methods: Comprehensive 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. Results: A 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. Conclusion: The 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.