Lower risk of developing systemic post-vaccination symptoms following first dose was independently associated with administration of mRNA vaccines vs. ChAdOx1 (aOR 0.29, 95% CI: 0.26–0.32 for BNT162b2 vs. ChAdOx1; aOR 0.06, 95% CI: 0.01–0.26 for mRNA-1273 vs. ChAdOx1), greater age (aOR per additional 10 years of age 0.85, 95% CI: 0.81–0.90), male vs. female sex at birth (aOR 0.59, 95% CI: 0.53–0.65), presence vs. absence of previous cancer (aOR 0.83, 95% CI: 0.71–0.97), use vs. no use of statins (aOR 0.84, 95% CI: 0.74–0.97), and use vs. no use of ACE inhibitors (aOR 0.80, 95% CI: 0.69–0.94). The gene discussed is ACE; the disease is cancer.