Zika Vaccines: Role for Controlled Human Infection

Zika virus (ZIKV), a previously little known arbovirus, caused an unprecedented outbreak in Latin America and the Caribbean throughout 2015 and 2016. The virus has been associated with the congenital Zika syndrome (CZS), which can occur with maternal ZIKV infection during any trimester and can result from asymptomatic infection. There is concern that even low levels of viremia can result in CZS, meaning an effective vaccine will need to induce very high levels of protection. Controlled human infection models (CHIMs), in which subjects are infected with a pathogen of interest, have been used to down-select vaccine candidates and have provided efficacy data in support of vaccine licensure. A ZIKV CHIM could be instrumental in determining which of the many ZIKV vaccine candidates provides the highest degree of protection and should be advanced in clinical development. The development of a ZIKV CHIM is not without challenges. The ZIKV, unlike other flaviviruses, is sexually and mosquito-transmitted, and an increase in the incidence of Guillain-Barré syndrome was reported in some countries during the ZIKV outbreak. These obstacles can be overcome with thoughtful study design to ensure maximal risk mitigation. If successful, a ZIKV CHIM could de-risk and accelerate ZIKV vaccine development.