US biotech company Inovio Pharmaceuticals said Wednesday it has had promising test results on a Zika virus vaccine in mice and plans to launch clinical trials on humans this year.

Inovio's SynCon technology "shows promise as a preventive and treatment" for Zika viral infections, said Inovio chief executive Joseph Kim.

Tests on mice offered promise in developing antibodies and "killer" T cells for countering the Zika virus.

"We will next test the vaccine in and initiate clinical product manufacturing," Kim said. "We plan to initiate phase I human testing of our Zika vaccine before the end of 2016."

About 15 pharmaceutical companies are working to develop vaccines for the previously obscure virus that has been linked to microcephaly, a birth defect that results in an abnormally small head and incomplete brain development, and Guillain-Barre syndrome, an immune system disorder.

The World Health Organization (WHO) declared the Zika outbreak an international health emergency on February 1 and said infections were reported in more than two dozen countries in South and Central America and the Caribbean, with Brazil the hardest hit.

Inovio, based in Plymouth Meeting, Pennsylvania, said Wednesday it would ask US regulatory authorities to accelerate the process for approving the vaccine with an eye towards marketing the medicine as quickly as possible.

Shares of Inovio rose 6.2 percent to $6.98 in late-morning trade.

A senior WHO official, Marie-Paule Kieny, said on February 12 there were two that appear most promising: one being developed by the US National Institutes of Health and another by India-based Bharat Biotech.

However, large-scale trials of these vaccines are still at least 18 months away, Kieny said.

The Zika virus, which is mainly carried by mosquitos, has spread rapidly through Latin America and the Caribbean, with multiple governments in the most affected areas urging women to avoid getting pregnant for the time being.