Fatal Human Rabies Infection with Suspected Host-mediated Failure of Post-Exposure Prophylaxis Following a Recognized Zoonotic Exposure—Minnesota, 2021

Background No rabies post-exposure prophylaxis (PEP) failure has been documented in humans in the United States using modern cell-culture vaccines. In January 2021, an 84-year-old male died from rabies six months after being bitten by a rabid bat despite receiving timely rabies post-exposure prophylaxis (PEP). We investigated the cause of breakthrough infection. Methods We reviewed medical records, laboratory results, and autopsy findings, and performed whole genome sequencing (WGS) to compare patient and bat virus sequences. Storage, administration, and integrity of PEP biologics administered to the patient were assessed; samples from leftover rabies immunoglobulin were evaluated for potency. We conducted risk assessments for persons potentially exposed to the bat and for close contacts of the patient. Results Rabies virus antibodies present in serum and cerebrospinal fluid were non-neutralizing. Antemortem blood testing revealed the patient had unrecognized monoclonal gammopathy of unknown significance. Autopsy findings showed rabies meningoencephalitis and metastatic prostatic adenocarcinoma. Rabies virus sequences from the patient and the offending bat were identical by WGS. No deviations were identified in potency, quality control, administration, or storage of administered PEP. Of 332 persons assessed for potential rabies exposure to the case patient, three (0.9%) warranted PEP. Conclusion This is the first reported failure of rabies PEP in the Western Hemisphere using a cell culture vaccine. Host-mediated primary vaccine failure attributed to previously unrecognized impaired immunity is the most likely explanation for this breakthrough infection. Clinicians should consider measuring rabies neutralizing antibody titers after completion of PEP if there is any suspicion for immunocompromise.