Pernicious Anemia Following ChAdOx1 nCoV-19 Vaccination in a Previously Healthy Adult: A Case Report

Abstract Background: COVID-19 vaccines have demonstrated a favorable safety profile and have been critical in reducing morbidity and mortality from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Although most adverse events are mild and self-limited, rare immune-mediated conditions temporally associated with vaccination have been reported. Pernicious anemia (PA) is an autoimmune disorder characterized by vitamin B₁₂ malabsorption due to antibodies against intrinsic factor (IF) and is infrequently described in this context. We report a case of symptomatic vitamin B₁₂ deficiency due to PA occurring shortly after ChAdOx1 nCoV-19 (AstraZeneca) COVID-19 vaccination. Case Presentation: A 39-year-old previously healthy woman developed progressive fatigue, light-headedness, and exertional dyspnea three weeks after receiving her second dose of the ChAdOx1 nCoV-19 (AstraZeneca) COVID-19 vaccine. Laboratory investigations revealed macrocytic anemia (hemoglobin 100 g/L; mean corpuscular volume [MCV] 111 fL), severe vitamin B₁₂ deficiency (90 pmol/L), and markedly elevated lactate dehydrogenase (LDH). Anti-intrinsic factor (IF) antibodies were positive. Upper gastrointestinal endoscopy demonstrated fundic atrophic gastritis, and bone marrow examination confirmed megaloblastic erythropoiesis. The patient was treated with intramuscular hydroxocobalamin, resulting in complete clinical and hematologic recovery during follow-up. Conclusion: This case describes Pernicious anemia (PA) presenting in close temporal association with COVID-19 vaccination in a previously healthy individual. Although causality cannot be established, the temporal relationship raises the possibility of immune activation contributing to disease onset. Early recognition and prompt vitamin B₁₂ replacement led to full recovery and may prevent irreversible neurologic complications.