Background: In Canada, young adults remain one of the least vaccinated adult age groups against COVID-19. As such, targeting vaccine messages towards this demographic is important for encouraging them to get vaccinated. Because young adults are a prominent user group on social media, we sought to understand if the vaccine messages from Canadian federal actors on Instagram were effective in promoting vaccine uptake based on best practices. Best practice messaging strategies include implementing guiding principles for crisis communication (i.e., transparency, compassion and empathy, conversational tone, clarity, correction of misinformation, call to action) and addressing the 5C model for vaccine hesitancy (i.e., complacency, confidence, risk calculation, constraints, collective responsibility). Methods: We performed a content analysis on 159 Instagram posts that mentioned COVID-19 vaccines from eight key federal accounts. In addition, we performed a sentiment analysis on the comment sections of these posts to understand public reaction to the messages being shared. Results: Across the 8 federal accounts and 159 Instagram posts that mentioned COVID-19 vaccines, federal actors did not widely incorporate best practices for vaccine communication. Further, the accounts did not adopt a unified approach to vaccine communication, and overall public sentiment was neutral. Conclusions: Our assessment has highlighted gaps in the social media communication strategy for COVID-19 vaccines. As such, these Results can encourage future vaccine communication campaigns that reach young adults to be informed by best practices and strategies to encourage vaccination.