Safety of equine tetanus antitoxin for prophylactic use in Ethiopia: a retrospective multi-center study

Tetanus remains a severe life-threatening infectious disease and neurological disorder in many parts of the world, where immunization programs are suboptimal. Any human injury or trauma has the possibility of getting infected with Clostridium tetani which is the sole causative bacterium of tetanus. Evidence is available that TAT may cause anaphylaxis and late serum sickness, while there has been no study conducted in Ethiopia. The Ethiopian Ministry of Health standard treatment guideline recommends tetanus prophylaxis for all tetanus-prone wounds. This study aimed to evaluate the safety of TAT administration in adults exposed to tetanus-prone wounds in Ethiopia.

The target product of this study was the equine tetanus antitoxin developed and manufactured by the ViNS Bioproducts Limited, India (Code: 130202084, A.W.No: 15/AAW/PI/02.00, DT: 25.04.2016). The product is delivered with the dose of 1000/1500 IU intramuscularly or subcutaneously to individuals at risk of tetanus infection for prophylactic purposes. The study was carried out in 11 healthcare facilities in Addis Ababa, Ethiopia, that had a relatively high clients load for tetanus-prone wounds. Medical records of patients with tetanus-prone wounds who received the equine TAT were reviewed retrospectively for any adverse events following immunization according to the World Health Organization (WHO) definition for adverse events following immunization (AEFI).

There were more than 20,000 patients treated for trauma in the facilities from 2015 to 2019. Upon revision of available registration books, we identified 6000 charts to be eligible for the study, of which 1213 charts that had complete and reliable data on the AEFI profile of the TAT were included in the final analysis. The median age of the study participants was 26 years (IQR = 11 years, age range: 18-91 years) and 78% (949) were male. The tetanus-prone wounds resulted mainly from stab (44%, 535) and blunt force (30%, 362), and the most common sites of wounds were hand (22%, 270) and head (21%, 253). The most and least frequently occurring types of wounds were open wounds (77%, 930) and organ system injury (0.003%, 4), respectively. The mean time of presenting at health facilities from the onset of trauma was 2.96 h. Of the total 1231 participants, one male participant who presented within 3 h after experiencing a wound on his nose at the workplace had a severe local reaction immediately after injection of the TAT. No AEFI was recorded for the other participants.

The adverse event following immunization of the equine tetanus antitoxin produced by the ViNS Bioproducts Limited was very rare. A regular review of the product's safety performance and systematic collection and analysis of adverse event reports are important to ensure the safety of the product.