CDC is indicating that Zika in the US could become more widespread than previously thought.
CDC has a fact sheet on what is known about sexual transmission
It is not known if men can get it from women, for example (with HIV, it was usually much more transmissible from men than women, but HIV was never shown to be transmitted by insects). It is not known if it lasts much longer in semen. In theory, if a different mosquito could pick up the virus from an infected person (even asymptomatic) before biting another person (especially a pregnant woman) this would have major "ethical" consequences since it could sustain much longer chains of transmission, but this doesn't (yet) appear to happen very much (or at all in the US).
Republicans are still squawking on appropriating more money, wanting to use Ebola money. Research is needed to develop and test a vaccine and perhaps anti-viral therapies.
But the damage to unborn children may be more extensive than thought, and the entire pregnancy period may be at risk. Milder learning and development disorders, not appearing until well into childhood or adolescence, may result, as well as microcephaly.
Adults usually don’t get very sick, but Guillain- Barre could turn out to be more common than expected, as well as other possible auto-immune disorders like multiple schlerosis. .
Widespread epidemics and birth defects in low income communities in the Gulf Coast areas, as well as Florida, and the Caribbean are feared.
The breakdown of transmission in the US and territories is shown in this CDC link.
The Guardian has a detailed store here. The public health measures later could get interesting, but I don't think the numbers are that alarming yet.
But novel viruses are always possible (as in my own novel draft). But a pandemic is more likely to come from an avian influenza or possibly a SARS-like disease than anything else. (Viruses very much like the SARS corona virus are rather common and most of them cause only minor infections, like around the larynx.)