During the course of her career, Messonnier notably worked on the 2001 anthrax attacks response, serving as co-leader of the anthrax management team and vaccine working group. She also played a leading role developing a low-cost meningococcal meningitis vaccine to prevent an emerging epidemic in Africa, known as MenAfriVac, in 2010. She has also worked on communications strategies to promote the use of vaccines to prevent the emergence of disease outbreaks.