A new study finds that people who have antibodies to the mosquito-borne Zika virus are more vulnerable to developing dengue disease. This immune interaction, called antibody-dependent enhancement, could complicate the search for a safe and effective vaccine that protects against Zika without also increasing the risk of dengue.

The study, which drew on data from two cohorts of Nicaraguan children who lived through a Zika epidemic in 2016 and a dengue epidemic in 2019, is the first to investigate the impacts of Zika immunity on dengue disease in humans.

Its findings confirm earlier suspicions that some antibodies to the Zika virus, which usually serve to protect the body from infection, may actually interact with dengue viruses in ways that can make dengue infection worse. This interaction, known as antibody-dependent enhancement, could make it harder for researchers to design a safe and effective vaccine that protects against Zika without also increasing the risk of dengue.

«The key thing that our study establishes is that prior Zika infection does significantly increase your risk of both symptomatic and more severe forms of dengue disease,» said study first author Leah Katzelnick, who performed the research as postdoctoral scholar at the University of California, Berkeley’s School of Public Health. «That finding raises the questions: Could a vaccine only targeted at Zika actually put people at increased risk of more severe dengue disease? And how can you design a Zika vaccine that only induces good antibodies that protect you against Zika, but doesn’t induce these other, potentially enhancing antibodies that are harmful against disease?»

A family of related viruses

Dengue disease is caused by not one but four closely related types of flaviviruses, each of which can strike with a slightly different set of symptoms and severity. Getting sick with one type of dengue virus can increase the likelihood that a person will develop a second, more severe illness when infected with a separate type of dengue virus. However, after a person has been infected with two types of dengue viruses, they usually gain some degree of immune protection against future dengue disease severity.

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Materials provided by University of California — Berkeley. Original written by Kara Manke. Note: Content may be edited for style and length.