The precise mechanism of how vaccines work is not always known. This is the case with the insect-based chimeric alphavirus vaccine against the Eilat (EILV)/chikungunya (CHIKV) virus. The CHIKV virus causes both acute and chronic infections in people, and an effective vaccine is needed. In a current study the mechanism of action of a EILV/CHIKV vaccine and live attenuated CHIKV181/25 vaccine were investigated, looking at the immune pathways activated by the vaccines in cynomolgus macaques. 

Core body temperature measured during viral challenges
Scientists from the University of Texas Medical Branch (UTMB), Experimental Pathology Laboratories, University of Missouri, and SUNY Upstate Medical University, all in the USA, implanted all cynomolgus macaques in the study intra-abdominally with Star-Oddi’s DST micro-T temperature loggers. The loggers were programmed to take temperature measurements every 15 minutes throughout the study. The implantation was done 20 days prior to the first viral challenge in the first study, and at the time of vaccination and 14 days prior to the viral challenge in the second study. In the graph below from Fig. 1, the temperature variations during the first study challenge period are shown, and Fig. 4 from the second study.

Single dose of EILV/CHIKV vaccine induces superior T-cell response
Vaccination of cynomolgus macaques with a single dose of EILV/CHIKV vaccine gave protection for up to a year. Various analyzes show adaptive immunity including T-cells and B-cells, as well as antibody response. This provides a long term and specific response against viral infection. The CHIKV 181/25 also induced powerful protection against a viral infection, however, through different T and B cell responses. The EILV/CHIKV response was shown to be superior T cell immunity that was sustained after one year. Compared to the CHIKV 181/25 memory B-cell response, which declined after one year. 

Further results can be viewed in the article published in NPJ Vaccines and can be accessed here.