Acute exacerbations of Myasthenia Gravis (MG) may be triggered by infections and certain drugs. No consensus has been reached on vaccines and the risk for developing myasthenic crisis. During the COVID-19 pandemic, MG patients are considered at high risk for severe illness, and vaccination is strongly recommended. We report the case of a 70-year-old woman with MG, diagnosed 2 years earlier, that developed myasthenic crisis 10 days after the second dose of the BNT162b2 mRNA COVID-19 vaccine (Pfizer-BioNTech). The patient had no previous MG exacerbations in her history. Following increase of oral pyridostigmine and prednisone treatment, the patient underwent immunoglobulin and plasma exchange therapy. Due to persisting symptoms, immunotherapy was switched to rituximab, under which a clinical remission was achieved. MG patients infected with SARS-CoV-2 may develop severe acute respiratory distress syndrome and have a higher mortality compared to the general population. In addition, reports of new-onset MG following COVID-19 infection accumulate. By contrast, since the beginning of the vaccination program, only 3 cases of new-onset MG after COVID-19 vaccinations have been published and 2 cases of severe MG exacerbation. Vaccinations in MG patients have always been debated, but most studies confirm their safety. In the era of COVID-19 pandemic, vaccination protects against infection and severe illness, especially in vulnerable populations. The rare occurrence of side effects should not discourage clinicians from recommending COVID-19 vaccination, but close follow-up of MG patients is recommended during the post-vaccination period.