An Anonymous Coward writes:
The Zika virus has been known for quite some time, but it gained notoriety recently due to its possible linkage to birth defects.
Science News has a summary report on Zika virus: https://www.sciencenews.org/article/special-report-heres-what-we-know-about-zika
A report on the studies of its possible linkage to microcephaly, a birth defect of babies with undersized and underdeveloped brains: https://www.sciencenews.org/article/how-zika-became-prime-suspect-microcephaly-mystery
In short, studies are continuing, evidence is mounting, but still not quite a confirmation.
The country urged women not to get pregnant until 2018... e.g. Daily Mail [dailymail.co.uk], Refinery29 [refinery29.com], Volkskrant [volkskrant.nl], etc.
Just imagine a situation where you feel advising people not to get pregnant for 2 years is better than the effect that THAT will have on your nation. For El Salvador, apparently, current evidence linking Zika to birth defects is good enough.