Does an earlier dengue infection protect children from Zika?
Children who had caught dengue before were no less likely to be infected by Zika, but when infected they were about a third less likely to get sick with symptoms.
Source
Prior dengue virus infection and risk of Zika: A pediatric cohort in Nicaragua
Study at a glance
- Design
- Cohort — Prospective community-based pediatric cohort (running since 2004) followed through the 2016-2017 Zika epidemic, with symptomatic cases tested at a health center and inapparent infections detected by paired annual blood samples.
- N
- N=3027 · 3,893 children took part during the study period; 3,027 with known dengue histories were in the symptomatic Zika analysis; 2,659 of these with paired annual sera were in the infection analysis.
- Population
- Children aged 2-14 years in a low-to-middle income district of Managua, Nicaragua
- Outcome
- Incidence of symptomatic Zika, incidence of total Zika virus infection, and the proportion of infections that were symptomatic, by prior dengue infection status
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What they did
The researchers used a long-running dengue cohort of 3,893 children in Managua, Nicaragua, whose past dengue infections had been recorded for years. When Zika arrived in 2016, sick children were tested at the study health center, and yearly blood samples before and after the epidemic revealed silent (inapparent) infections. They compared Zika infection and symptom rates between children with and without earlier dengue, adjusting for age and sex.
What they found
Zika was very common: 560 children had symptomatic Zika, and total infection incidence was roughly 36.5 per 100 person-years. Prior dengue did not change the chance of being infected with Zika (IRR 0.98), but among infected children it lowered the rate of having symptoms (IRR 0.62), and it lowered the overall rate of symptomatic Zika (IRR 0.63). Girls and older children had higher rates of infection, and the early reproduction number was estimated at about 3.3-3.4.
The limits
What it doesn't show
The study included only children, so it cannot say whether dengue immunity protects adults, and it did not examine serious outcomes such as birth defects or Guillain-Barre syndrome. Some children were excluded because their dengue histories or paired blood samples were incomplete, and infections were partly classified by a serological algorithm that could misclassify some cases. Symptomatic infections were only caught if families came to the health center, and shared mosquito exposure is an unmeasured confounder. As an observational study, it shows an association, not proof that dengue antibodies or T cells cause the protection.
Key terms
- Inapparent infection
- An infection that produces no noticeable symptoms but can be detected afterwards because the person develops antibodies.
- Incidence rate ratio (IRR)
- The rate of new events in one group divided by the rate in a comparison group; values below 1 mean fewer events in the first group.
- Cross-reactive immunity
- Immune responses made against one virus that also recognise a closely related virus, such as dengue and Zika, which are both flaviviruses.
- Effective reproduction number (Re)
- The average number of people each infected person goes on to infect at a given point in an epidemic.
- Seroconversion
- A change from having no detectable antibodies to a pathogen to having them, showing that an infection occurred between two blood samples.
Flashcards
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Quiz yourself
What was the association between prior dengue and the risk of becoming infected with Zika?
Common questions
Why did the authors look at symptoms among infected children separately?
Children who had dengue may simply live where mosquitoes bite more, which would push up their infection risk. Looking only within children already infected with Zika removes that exposure difference, and the protective estimate stayed about the same.
Does this mean dengue infection is good for you?
No. Repeat dengue infection with a different serotype is a major risk factor for severe dengue. The finding is only that earlier dengue was linked to fewer Zika symptoms, not that dengue infection is beneficial overall.
Why is a cohort study better than a case-control study for this question?
Because each child's dengue history was recorded before Zika arrived, the exposure was measured prospectively and not recalled after illness, which reduces recall and selection bias.
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