The US Food and Drug Administration (FDA) has approved the first human tests of an experimental Zika virus vaccine, the makers of the drug announced on Monday.

Called GLS–5700, the medication will be used in a clinical trial involving 40 healthy people, and represents the first major step towards ultimately immunising people against Zika – which was declared a global public health emergency by the World Health Organisation (WHO) in February.

"We are proud to have attained the approval to initiate the first Zika vaccine study in human volunteers," said J. Joseph Kim, president and CEO of US-based Inovio Pharmaceuticals, which is developing the vaccine with South Korean partner, GeneOne Life Science. "We plan to dose our first subjects in the next weeks and expect to report phase 1 interim results later this year."

GLS–5700 works by stimulating the body's immune system to defend itself against Zika. Synthetic fragments of viral DNA are injected into the skin, prompting the immune system's T cells to generate antibodies to fight the infection.

The news of the vaccine trial comes two months after the US Centres for Disease Control and Prevention (CDC) confirmed the causative link between the infection and birth defects such as microcephaly, and represents the culmination of an intense nine months of vaccine development, during which global fears over Zika's spread have only grown.

"As of May 2016, 58 countries and territories reported continuing mosquito-borne transmission of the Zika virus," said Kim. "[T]he incidences of viral infection and medical conditions caused by the virus are expanding, not contracting."

It's worth pointing out that just because GLS–5700 has reached human testing, there's no guarantee it will turn out to safely immunise people against Zika. The vaccine has been tested successfully in small and large animal models, but clinical trials in humans could take several years to demonstrate that the treatment is safe, and there's no guarantee it will ultimately prove effective or make it through subsequent testing phases.

But fortunately, GLS–5700 isn't the only Zika vaccine candidate currently in development. An Indian company called Bharat Biotech is researching Zika vaccine development in animals, while French pharmaceutical company Sanofi SA is expected to begin human trials with one of its drugs later this year.

In the US, the National Institute of Allergy and Infectious Diseases (NIAID) says it's expecting to shortly receive FDA approval to trial a separate vaccine candidate it developed itself, which would mean we could have two vaccines in human testing in a matter of weeks.

Earlier in the month, scientists from the University of Texas Medical Centre published findings on how a protein called interferon-induced protein 3 could help reduce Zika's ability to infect brain cells – although clinical trials may be a while away for that particular treatment.

Even though there's a huge amount of hurdles and potential roadblocks facing all of these vaccine trials, there's reason to have hope.

"Always, the first vaccine to go into clinical trial is important," epidemiologist Anna Durbin from Johns Hopkins University, who is involved with the NIAID vaccine effort, told Jessica Glenza at The Guardian.

"It means the FDA has reviewed it, and I'm sure is formulating questions and getting ready for additional candidates to submit their investigational drug applications," she added. "It shows progress and momentum, and we just need to keep momentum going."