October 3rd 2016; updated on January 9th 2017
Early September, Minister of Health in Colombia declared end of Zika outbreak. With 78.000 suspected /7166 confirmed cases ; 21 microcephalies and 398 Guillain Barré Syndrome (GBS). It means prevalence for microcephaly estimated in a range of 2.7/10.000 to 29/10.000 at the time being. As of today we have 42 microcephalies recorded leading from 2.7/10.000 to 5.9/10.000 for the confirmed cases.

from @thelonevirologi
According to data, 7.9% microcephaly cases are linked/caused by Zika virus so far.
According to evidence based medecine, taking into account tested ZIKV + microcephaly cases, we get 17% of the entire microcephaly tested for ZIKV.
Question: if we all agree to say that Zika virus is involved in the immunological process leading to neural defect and microcephaly, we have to cope with other causes (83%) responsible for microcephalies. On a Global Health issue, it appears more and more obvious that studies are required to build a full picture of the root causes tree regarding microcephaly outbreak in South Americas. By comparing Brazil with Colombia, we might discover different paths to follow, especially by studying what happened in NE Brazil.
Colombia recorded a lot of GBS (>398) compared with microcephaly (>21). A interesting paper is just released in J.Autoimmun 2017 by Colombian researchers pointing out the role of Dengue antibodies. Socio-economics factors are also interfering in the process leading to neurological defects.
“All GBS patients were positive for IgG antibodies against both ZIKV and Dengue virus, and 69% were positive for Chikungunya virus.”
Some time ago, CDC and WHO have posted a statement on microcephaly caused by Zika virus. May be they jump the gun?