Adverse events following immunization with typhoid conjugate vaccine in an outbreak setting in Hyderabad, Pakistan

Pakistan is facing the world's largest outbreak of extensively drug-resistant (XDR) Typhoid. Vaccination campaign for children aged 6 months to 10 years old with Typhoid Conjugate Vaccine (Typbar-TCV®) was conducted in high-risk areas of Hyderabad during 2018. About 207,000 children were vaccinated. Here we report the adverse events following immunization (AEFI) during the campaign. The campaign was carried out using outreach and fixed centre strategy. Community mobilizers visited each household to perform line listing and mobilize parents with age-eligible children. Children were observed for 30 min post-vaccination. Two-pronged strategy was used for ascertainment of AEFI. A 24/7 hotline number was provided to all parents/caretakers (n = 199,861) to report AEFI during 14 days following immunization. An age-stratified (n = 7139 children) were actively followed at days 7 and 14 for the ascertainment of AEFI. All AEFI were examined by three trained medical officers. A structured questionnaire using Brighton collaboration criteria with level 3 diagnostic certainty was used for the recording of AEFI. Data were analysed using Microsoft Excel Office 365. Overall, 499 AEFI (433 in the subset actively followed and 66 self-reported through hotline) were observed. The rate of AEFI was significantly higher among very young children (age group 6 to 12 months) as compared to 2 to 3 years old children (0.54% vs. 0.33% respectively; p-value < 0.001). Fever was the most common AEFI self-reported through the hotline (38/199,861 = 0.02%) and among the subset followed actively for 14 days (206/7139 = 2.89%). Fever was followed by local reactogenicity 10/199,861(0.01%), and 134/7139 (1.88%) through self-reported hotline and active follow-up, respectively. No serious AEFI was observed. Administration of a single dose of Typbar-TCV among children aged 6 months to 10 years old during an outbreak setting of Hyderabad Pakistan was safe.