The 2015–2016 outbreak of Zika virus disease in the Region of the Americas demonstrated how a relatively obscure and mild mosquito-borne disease can become a global health emergency, causing congenital Zika syndrome, including microcephaly, and neurological complications such as Guillain-Barré syndrome.
On 1 February 2016, the WHO Director-General declared Zika virus and its associated complications a Public Health Emergency of International Concern. In her statement, Dr Margaret Chan, then the WHO Director-General, highlighted the urgent need for research and development (R&D) of preventative and therapeutic solutions for Zika virus disease. In the period since this call to action, the global research community responded with introduction of 45 vaccine candidates in the R&D pipeline, some of which have moved into human clinical trials. The current landscape of Zika virus vaccines and therapeutics was reviewed in a recent article published in BMC Medicine1.
Studies in animal models have shown promising results of Zika virus vaccines for preventing maternal-fetal transmission and generating immunity in the vaccine recipient, but further validation is still required in clinical settings. Several vaccine candidates are currently in phase 1 and 2 of human clinical trials, summarized in the WHO vaccine pipeline tracker.
Many hurdles remain, however, before a vaccine will become available. The limited number of cases occurring globally limits the ability of studies to evaluate the protective effects of vaccines in phase 3 human trials. To prepare sites for future clinical trials, mathematical modelling is being used to predict when and where potential future Zika outbreaks may occur, but accurately predicting and preparing sites for future multi-centre clinical trials present unique logistical challenges. In the absence of a suitable population and/or environment to test a candidate vaccine, other options for clinical evaluation are being considered.
The authors highlight that therapeutics for Zika virus infection, which are also in development, could be advanced in tandem with vaccine development, in an effort to further reduce the burden of disease. Therapeutics could be used as prophylaxis, and reduce disease severity by accelerating viral clearance.
The authors emphasize the critical need for sensitive, specific, and reliable diagnostic tests for Zika virus infection, in order to assess vaccine efficacy and clinical trial endpoints of candidate vaccines.
Discovery of vaccines for this newly-emerged pathogen will require sustained commitment and investment. Continued financial support and engagement of industry, researchers, and public health partners will be needed for the successful development, licensure, and accessibility of Zika vaccines and therapeutics.
1 Zika vaccines and therapeutics: landscape analysis and challenges ahead
Wilder-Smith A, Vannice K, Durbin A, Hombach J, Thomas SJ, Thevarjan I, Simmons CP. BMC Med. 2018 Jun; 16(1):84.