Investigating the association between yellow fever vaccination and symptomatic acute Zika virus infection: a case-control study.

BACKGROUND

During the Zika virus (ZIKV) epidemic in Latin America (2015-2016), a high incidence of microcephaly was observed in places with low yellow fever (YF) vaccination coverage. Cross-reactivity between ZIKV and YF virus was hypothesized as a possible explanation.

METHODS

We performed a case-control study to estimate the odds of ZIKV infection according to patients' YF vaccination status. The study considered ZIKV fever as the outcome, and previous vaccination against YF as exposure. We included all confirmed cases of acute ZIKV fever in Campo Grande, Mato Grosso do Sul, from January 2015 to December 2018. The control group comprised age- and sex-matched residents of Campo Grande who had no history of acute febrile arboviruses during the study period.

RESULTS

The cumulative incidence of acute ZIKV fever was 1.87 cases per 1000 population. The case group had a predominance of women aged 20-39 years and white and mixed races. Vaccination coverage for YF was 65.5% in the case group and 60.9% in the control group. The odds ratio (OR) suggested a weak association between outcomes and exposure (OR = 1.23; 95% confidence interval [CI]: 1.05-1.44).

CONCLUSIONS

Our findings provide no evidence that prior YF vaccination protects against acute ZIKV infection. Further studies are needed to analyze the development of anti-ZIKV and anti-YF neutralizing antibodies in affected individuals because new ZIKV epidemics are predicted.