The Short Version
The evidence does not support the broad assertion that MTHFR mutations increase adverse reaction risk across vaccines generally. The only direct peer-reviewed finding linking MTHFR to vaccine adverse events comes from a single 2008 smallpox vaccination study — a vaccine no longer in routine use. The most current synthesis, a 2023 systematic review, found data too sparse for firm conclusions and identified only a "possible association." Clinical institutions do not recognize MTHFR status as a contraindication or established risk factor for vaccination.