Adverse Event Following COVID-19 vaccination in Thailand (1/3/2021–31/12/2021), 10 months experiences after the nationwide campaign

Abstract

Background: COVID-19 vaccines have been introduced for emergency use in Thailand to combat with COVID-19 pandemic since 1/3/2021. When mass vaccination campaign is launched, the likelihood of adverse event following immunization (AEFI) reports is also increased. Here, we described the AEFI surveillance system and the situation of AEFI after the COVID-19 vaccination campaign.
Methods: We described the AEFI surveillance system. Moreover, we reviewed the AEFI-DDC database (a national program to monitor the serious AEFI cases) during 1/3/2021–31/12/2021 to describe characteristics of serious AEFI cases, and extracted vaccine administration data from the MOPH-IC (a national data base designed for COVID-19 vaccine registry). Descriptive statistics i.e., percent and rate per dose administration were calculated.
Results: The Ministry of Public Health has designated the committees for the nationwide COVID-19 vaccination campaign, including the committee to monitor vaccine safety. The members of AEFI expert committee have been expanded to cover all relevant areas such as cardiologist and hematologist. In addition, the regional AEFI expert committees have been designated to oversee the AEFI at the regional level, thereby, promptly responses to vaccination issue could be made. AEFI surveillance data showed that among the 104,444,169 doses administered, 6,396 were serious events (rate 6.12/100,000 doses), including 1,885 deaths (1.8/100,000 doses). The review of causality assessment data by the AEFI expert committee showed that most of the events were coincident (54%), followed by immunization stress related reaction (ISRR) (15%), vaccine product related reaction (8%); indeterminate (7%), unclassifiable (3%), and 12% were still waiting for more information. Among the vaccine related cases, most of them were hypersensitivity reaction. There were 7 vaccine induced thrombotic thrombocytopenia cases (0.01/100,000 doses), and 28 myocarditis cases (0.03/100,000 doses).
Recommendations: The majority of serious AEFI event were coincident. However, closely monitoring of the AEFI event is crucial to ensure the public on vaccine safety. In dept analysis on adverse event of special interest such as myocarditis, VITT, cardio and cerebrovascular events should be performed and compared with the baseline health data.