The COVID-19 vaccines can provoke a response from white blood cells, or T cells. The cells are believed to protect against COVID-19.

T-cells can theoretically trigger Mycobacterium leprae, a bacteria that causes leprosy, leading to leprosy or a leprosy reaction, the researchers said.

Other vaccines have been shown to trigger leprosy or leprosy reactions, including tuberculosis vaccines, and some people who receive repeated COVID-19 vaccinations have been shown to have weakened immune systems.