It's pretty close to the great big mass of purple on the CDC affected areas map [1], which are the areas where people are getting it (from actually being bitten by mosquitos). These mosquitos do live on Antigua, so much so that the local government is stepping up anti-mosquito measures [2]. They are on high alert for it and it's not too much of a leap to believe it will jump that short distance IMO. I'd also be concerned about the extensive use of insecticides in these areas affecting foetal development.
Regarding whether Zika does cause microcephaly: it's only a suspected link at the moment, but there does seem to be a strong correlation between this outbreak and the sharp increase in cases of microcephaly. Yes, it has been around for ages, but not at these levels. Hence limited data to determine the presence of a link.
An outbreak of Zika in French Polynesia in late 2013 saw a simultaneous 20-fold rise in Guillan-Barré syndrome [3] (which is an immune attack that causes damage to the nervous system). I'm not making the link, but it seems a little too coincidental to me that nervous system damage and stunted brain development have both been linked to Zika.
With respect to Phoenix85's comments on the change to the TDaP vaccine: have you found any credible sources for a link? You know, places that provide evidence from actual science? I can only find conspiracy theory anti-vaxxer websites...
Bear in mind the component parts of the vaccine will have had literally hundreds of millions of uses over a long period of time to be able to draw data from, to even hint at a link to any adverse effects.
Contrast that with a disease that historically has only presented a handful of cases, that appears to have caused neurological symptoms in some humans; now we're seeing a mass outbreak, that is coinciding with a marked increase in microcephaly in babies who were developing at that time.
Will the worry affect your holiday?
What's 9 months of not going to somewhere where there might conceivably be a serious life-changing risk, compared to the rest of your and your child's life?
It's up to you ultimately.
Refs available on request. PF doesn't like low-post-count-ers posting links...