Engineered Zika mRNA vaccine protects macaques without fuelling dengue 'enhancement'

A peer-reviewed study published online on 7 October 2026 in Cell Reports Medicine describes a Zika mRNA vaccine that protected macaques from Zika infection without the dangerous side effect that has troubled vaccines against this virus family.

The problem

Zika and dengue are related flaviviruses. Antibodies made against one can sometimes help the other infect cells — an effect called antibody-dependent enhancement (ADE), which can make a later dengue infection worse. This has been a major hurdle for vaccine development.

What the researchers found

• They used an mRNA vaccine in which the virus’s fusion loop — a region that tends to trigger cross-reactive antibodies — was engineered. Earlier tests of this approach had been limited to mice.
• In macaques, the vaccine protected against Zika challenge with negligible dengue ADE, the authors report.
• More than 97% of the vaccine-induced antibody-producing B cells were specific to Zika. Many used the monkey counterpart of a human antibody gene (IGHV5-10-1) that people also tend to use during natural Zika infection.
• Cryo-electron microscopy showed these antibodies hit a distinct vulnerable spot on the virus; a sugar group on the dengue version of that spot blocks them, which helps explain why they do not cross-react.

Limitations

This is a study in monkeys, not people. The vaccine has not been tested in humans, and results in animals often do not carry over fully. Larger and longer studies, and eventually clinical trials, would be needed before any such vaccine could be used.