COVID-19 Vaccine Timing and Co-Administration with Influenza Vaccines in Canada: A Systematic Review with Comparative Insights from G7 Countries

Background/Objectives: Despite significant advancements in vaccine development and distribution, the optimal timing and integration of COVID-19 vaccination in Canada remain crucial to public health. As the SARS-CoV-2 virus continues to evolve, determining effective timing strategies for booster doses is necessary to sustain immunity, especially in high-risk populations. This systematic review aims to critically evaluate the timing and co-administration strategies of COVID-19 vaccines in Canada, comparing them with approaches in other G7 nations. Method(s): The review seeks to identify best practices to inform national vaccination policies, with a particular focus on synchronizing COVID-19 and seasonal influenza vaccinations. We systematically searched Scopus, PubMed, Medline, and Web of Science (17 August 2021 to 7 July 2024) using the PECOS framework. Two independent reviewers screened titles/abstracts, extracted key data on immunogenicity, efficacy, and safety, and performed a narrative synthesis on timing and co-administration outcomes. Result(s): Evidence summarized across G7 countries reveals that most nations are converging on annual or flexible booster schedules tailored to high-risk groups, often aligning COVID-19 vaccination with influenza campaigns. Countries like Canada, the UK, and the US have integrated these efforts, while others maintain more independent or heterogeneous approaches. In addition, timely booster doses, whether administered annually or more frequently in high-risk settings, consistently reduce infection rates and hospitalizations. Conclusion(s): These findings collectively support the continued evolution of COVID-19 vaccination programs toward integrated, seasonally aligned strategies. Future public health efforts can build on these lessons not only to sustain protection against SARS-CoV-2 but also to strengthen preparedness for other respiratory infections. Copyright © 2025 by the authors.