Accepted for/Published in: JMIR Research Protocols
Date Submitted: Mar 3, 2023
Date Accepted: Jul 19, 2023
Efficacy and Safety of Smallpox Vaccine for Post-Exposure Prophylaxis in Mpox: Protocol for an Open-Labeled, Single-Armed Study
ABSTRACT
Background:
In May 2022, an mpox case with no history of overseas travel was reported in the United Kingdom, followed by reports of infections in Europe, the United States, and other countries worldwide. As immune responses are almost completely overlapping among viruses of the genus Orthopoxvirus (poxvirus, mpox virus, vaccinia virus, etc.), it is believed that cross-immunity can be achieved by vaccinating against the smallpox virus. In Japan, a smallpox vaccine (LC16m8 strain vaccine) has been approved for smallpox, but no vaccine has been approved for mpox.
Objective:
The first objective is to evaluate the efficacy of a vaccine approved in Japan against smallpox (LC16m8 strain vaccine) when administered to close contacts of mpox cases for prophylaxis against the disease. The second objective is to investigate the safety of the vaccine used for post-exposure prophylaxis against mpox.
Methods:
The target number of vaccinated subjects is set at 100 for those who have been identified as close contacts of mpox cases. After obtaining consent, the subjects are inoculated with the vaccine, and the symptoms (body temperature, headache, rash, and side effects) are recorded in the subjects' diaries every day until day 21 and on day 28. In addition, on days 7, 14, 21, and 28, the investigators investigate adverse events in the subject. Furthermore, on day 21 after close contact, the investigators observe the subject to confirm the onset of mpox. From the above results, the efficacy (prophylaxis effect against incidence and severity) and safety of the vaccine will be evaluated.
Results:
The first trial participant was enrolled on July 28, 2022. The research period is scheduled to run through March 2023. The study results will be published in a peer-reviewed scientific journal.
Conclusions:
This study will allow us to determine the efficacy and safety of the LC16m8 strain vaccine in the post-exposure prophylaxis against mpox. Clinical Trial: Japan Registry of Clinical Trials jRCTs031220137; https://jrct.niph.go.jp/re/reports/detail/26790
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