COVID-19 vaccine misinformation contributed to vaccine hesitancy and preventable illness. This study tested whether a brief online game helps Canadian adults identify COVID-19 vaccine misinformation, and whether effects last one month. In the game, participants judged whether statements about COVID-19 vaccines were true or false and immediately received the correct answer with a brief evidence-based explanation, delivered in a game-like format with points, ranks, and feedback. Adults from a national non-probability online panel (n = 4,071) were randomized to the game, to the identical corrective content presented as a static blog post, or to a no-activity control. The game and blog groups were assessed immediately after the activity; all three groups were reassessed approximately one month later. The hypothesis was that gamified corrective information would produce more accurate knowledge than the same information presented as a static blog post and, at one month, than no activity. The primary outcome was accuracy in identifying true and false claims; vaccination intention, vaccine confidence, and self-reported vaccination were secondary outcomes. This is the fourth study in a research program whose first three trials are registered in a companion record.