Logistic regression was conducted by taking worsening as dependent variable and patient characteristics (gender, onset age, onset muscle involvement, thymoma, and AChR or MuSK antibodies), age at first dose, interval since last aggravation, IBFD MGFA classes, IBFD PIS, and MGSTI score as independent variables, and it was revealed that interval since last aggravation ≤6 months was the only independent factor associated with worsening after vaccination (P = 0.01, OR = 8.62, 95% CI: 1.93–38.46). The gene discussed is MUSK; the disease is thymoma.