Washington, Jan 29 (IANS): The US researchers are working on two potential vaccines for the Zika virus, but warned that it will likely take years before these are ready for use, a senior US health officials said.

Both the candidates were based on earlier vaccines related to the viruses of West Nile and dengue, with one ready for clinical trial later in 2016, Xinhua quoted Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, as saying on Thursday.

Zika, transmitted primarily through the bite of an infected Aedes species mosquito, is believed to cause birth defects such as microcephaly, or small heads.

Currently, there is no vaccine to prevent or medicine to treat the disease.

"While these approaches are promising, it is important to understand that we will not have a widely available safe and effective Zika vaccine this year and probably not even in the next few years," Anthony Fauci said.

Anne Schuchat, principal deputy director of the US Centres for Disease Control and Prevention, said her agency has identified 31 travel-related cases of Zika virus in the US.

All of the cases involved people returning to the US from countries where the Zika virus is spreading, she said.

Meanwhile, the US Food and Drug Administration said it was working to rapidly implement appropriate donor deferral measures for travellers who have visited affected regions in order to protect the blood supply.

About one in five people infected with Zika virus will develop symptoms which include fever, rash, joint pain, and pink eye.

The illness is usually mild with symptoms lasting from several days to a week. Severe disease requiring hospitalisation is uncommon and the case fatality rate is low.