Age-specific chikungunya outbreak response immunisation strategies in Brazil: a modelling study

Area of Science:

• Epidemiology
• Public Health
• Vaccinology

Background:

• Two chikungunya vaccines, Ixchiq and Vimkunya, are licensed.
• Brazil is the first endemic country to license Ixchiq, but optimal vaccination age groups are unclear.

Purpose of the Study:

• To model the public health impact of age-specific chikungunya outbreak response immunization strategies in Brazil.
• To infer broader implications for vaccine use in outbreak-prone regions.

Main Methods:

• Developed an age-structured transmission dynamic model calibrated with Brazilian surveillance data.
• Simulated outbreak response immunization strategies targeting various age groups (1-11, 12-17, 18-59, ≥60 years).
• Assessed vaccine impact by symptomatic cases, deaths, DALYs averted, and NNV, considering protection against disease and infection.

Main Results:

• Ixchiq and Vimkunya demonstrated similar vaccine impact.
• Vaccinating children 1-11 years yielded the lowest NNV.
• Vaccinating adults 18-59 years achieved the greatest reduction in symptomatic cases (62.5-66.2%) and DALYs averted.

Conclusions:

• Under current licensure, vaccinating adolescents (12-17) followed by adults (18-59) are efficient strategies for Ixchiq and Vimkunya.
• Expanding eligibility to younger populations (1-11 years) could increase vaccination efficiency.