Zika virus infection, associated microcephaly, and low yellow fever vaccination coverage in Brazil: is there any causal link?

Abstract

Introduction: Since the end of 2014, Zika virus (ZIKV) infection has been rapidly spreading in Brazil. Methodology: To analyze the possible association of yellow fever vaccine with a protective effect against ZIKV-related microcephaly, the following spatial analyses were performed, using Brazilian municipalities as units: i) yellow fever vaccination coverage in Brazilian municipalities in individuals aged 15-49; ii) reported cases of microcephaly by municipality; and iii) confirmed cases of microcephaly related to ZIKV, by municipality. SaTScan software was used to identify clusters of municipalities for high risk of microcephaly. Results: There were seven significant high risk clusters of confirmed microcephaly cases, with four of them located in the Northeast where yellow fever vaccination rates were the lowest. The clusters harbored only 2.9% of the total population of Brazil, but 15.2% of confirmed cases of microcephaly. Conclusion: We hypothesize that pregnant women in regions with high yellow fever vaccination coverage may pose their offspring to lower risk for development of microcephaly. There is an urgent need for systematic studies to confirm the possible link between low yellow fever vaccination coverage, Zika virus infection and microcephaly.

Zika virus pathogenesis in rhesus macaques is unaffected by pre-existing immunity to dengue virus

“…The Brazilian cohort showed that 29% of women with ZIKV infection at any time during pregnancy had abnormalities in prenatal ultrasonography, while the French Polynesia study suggested that only 1% of fetuses and infants from women who had ZIKV infection during the first trimester of pregnancy developed microcephaly. These and other observations have stimulated discussion and raised questions about the role of pre-existing flavivirus immunity in ZIKV pathogenesis especially during pregnancy2122.…”

Yellow Fever Vaccine Protects Resistant and Susceptible Mice Against Zika Virus Infection

“…A recent epidemiological study reports that preexisting infection with dengue virus (as determined by high antibody titers) was associated with reduced risk of ZIKV infection (34). Also, based on epidemiological data, it has been suggested that pregnant women in regions of Brazil with lower YFV vaccination coverage are at higher risk for the development of microcephaly (15). However, no experimental evidence has been provided for this hypothesis.…”

“…It is possible that the YFV vaccine may be effective in protecting humans against ZIKV, especially against neurological diseases in adults and congenital Zika syndrome. Based on epidemiological data, it has been suggested that pregnant women in regions of Brazil with lower YFV vaccination coverage are at higher risk for the development of microcephaly (15).…”

“…In the event that an already licensed vaccine effectively protects against ZIKV infection, several steps in the development of a new vaccine candidate could be skipped, and the vaccine already available on the market could be used. Northeastern Brazil was the region with the highest incidence of microcephaly between October 2015 and March 2015 and low coverage of YFV vaccination (15).…”

From the perception of a cluster of cases of children with microcephaly to congenital Zika syndrome in Brazil: the lessons we have learned and the challenges that lie ahead of us

“…We are no longer talking about a single disease transmitted by a unique vector, but also by sexual contact and possible transmission by saliva, transfusion, breast milk, sweat and tears [7–12]. The Zika virus infection that initially appeared to be harmless is now of devastating consequences and many doubts remain [13, 14]. What is the real cause for the higher occurrence in northeastern Brazil?…”