Evaluating Vaccination Strategies for Zika Virus in the Americas

Abstract

Background Mosquito-borne and sexually-transmitted Zika virus infection has become widespread across Central and South America as well as in the Caribbean. Over 30 Zika vaccine candidates are under active development. Objective To quantify the impact of Zika vaccine prioritization of females aged 9–49, followed by males aged 9–49, on the incidence of prenatal Zika infections. Design We developed a compartmental model of Zika transmission between mosquitoes and humans calibrated to empirical estimates of country-specific mosquito density. Mosquitoes were stratified into susceptible, exposed, or infected classes; humans were stratified into susceptible, exposed, infected, recovered, or vaccinated classes. We further incorporated age-specific rates of fertility, Zika sexual transmission, and country-specific demographics. Setting 34 countries or territories in the Americas with documented Zika outbreaks. Target population Males and females aged 9–49. Interventions Age- and gender-targeted immunization using a Zika vaccine with efficacy ranging from 60–90%. Measurements Annual prenatal Zika infections Results For a base-case vaccine efficacy of 75% and vaccination coverage of 90%, immunizing females aged 9–49, the WHO target population, would reduce the incidence of prenatal infections by at least 94%, depending on the country-specific Zika attack rate. In regions where an outbreak is not expected for at least ten years, vaccination of females aged 15–29 is more efficient than vaccinating women over 30 years. Limitations Population-level modeling may not capture all local and neighborhood-level heterogeneity in mosquito abundance or Zika incidence. Conclusions A Zika vaccine of moderate to high efficacy has the potential of virtually eliminating prenatal infections through a combination of direct protection and transmission reduction. Efficiency of age-specific Zika vaccination targeting depends on timing of future outbreaks. Funding National Institutes of Health

Impact of age-specific immunity on the timing and burden of the next Zika virus outbreak

“…Other ZIKV vaccination studies confirm our findings. However, they do not show the effect in risk groups nor assume herd immunity from previous outbreaks like we did here; Durham et al (2018) showed that immunizing females aged 9 to 49 years with a 75% effective vaccine and a coverage of 90%, would reduce the incidence of prenatal infections by at least 94%. Similarly, Bartsch et al (2018) showed that women of childbearing age or young adults would be an ideal target group for vaccination Valega-Mackenzie and Ríos-Soto (2018).…”

Impact of age-specific immunity on the timing and burden of the next Zika virus outbreak

“…Other ZIKV vaccination studies confirm our findings. However, they do not show the effect in risk groups nor assume herd immunity from previous outbreaks as we did; Durham et al (2018) showed that immunizing females aged 9 to 49 years with a 75% effective vaccine and a coverage of 90%, would reduce the incidence of prenatal infections by at least 94% [41]. Similarly, Bartsch et al (2018) showed that women of childbearing age or young adults would be an ideal target group for vaccination [42].…”

Evolution of Two Major Zika Virus Lineages: Implications for Pathology, Immune Response, and Vaccine Development

“…A successful ZIKV vaccine must confer strong protection in healthy and pregnant populations, while also proving safe and efficacious in regards fetal/neonatal health. Important features to consider for the best vaccine should include both enhanced magnitude and quality of neutralizing antibodies and minimal cross-reactivity to DENV to prevent antibody-dependent enhancement (ADE) ( 146 – 149 ). ADE is perhaps the most critical of these, as flaviviruses are antigenically and structurally similar, non-neutralizing antibodies generated by one flavivirus can result in fatal outcomes upon secondary infection with a different flavivirus.…”