Since the World Health Organization declared Zika a public health emergency in February, teams of scientists from all over the world have been attacking the virus from many different angles. They have made advances in understanding the structure of the virus, the historical path of the mosquitoes that carry it and the risk to babies still in the womb — important knowledge, but of little immediate practical use.

Now, the discoveries have finally led to something that might be able to stop the pathogen: a vaccine.

Pennsylvania vaccine maker Inovio Pharmaceuticals and South Korea’s GeneOne Life Sciences said Monday that they had received approval from U.S. regulators to start testing a DNA vaccine, known as GLS-5700, on humans. The early-stage study will include 40 healthy subjects. It is primarily designed to assess the safety of the vaccine but will also measure the immune response generated by the injection. Zika, part of the flavivirus family of viruses that includes West Nile, dengue and yellow fever, is believed to be responsible for causing thousands of babies to be born with shrunken heads in Brazil and elsewhere. The Centers for Disease Control and Prevention recently detailed the cases of six babies born with the condition in the United States.

Inovio chief executive J. Joseph Kim said the company, which is also working on vaccines for other devastating global viruses such as Ebola and Middle East Respiratory Syndrome (MERS), will begin the tests in the next few weeks and expects to report results later this year.

“We are proud to have attained the approval to initiate the first Zika vaccine study in human volunteers,” Kim said in a statement. “As of May 2016, 58 countries and territories reported continuing mosquito-borne transmission of the Zika virus; the incidences of viral infection and medical conditions caused by the virus are expanding, not contracting.”

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has said he believes the world’s best hope against Zika is a vaccine and that, because of previous research on West Nile and dengue, a Zika vaccine should take less time to develop than vaccines for many other infectious diseases. The challenge is that Zika is unique among its related viruses because the others don’t invade the nervous system or developing fetuses because of blood-brain and placental barriers.

Researches who examined the virus’s structure with an electron microscope recently explained to The Washington Post what it is about its structure that might make it so dangerous:

It shares a basic structure with all flaviviruses: Genetic info in the form of RNA is surrounded by a fatty membrane, then encased in a protein shell with a 20-sided face. The protein shells are made of 180 copies of two different proteins, each composed of chains of different amino acids. Once inside a target cell, the virus breaks apart and forces the host to do its bidding, replacing the instructions coded into the cell’s DNA with those programmed by viral RNA.

Zika differs most from other flaviviruses at a spot thought to be crucial to the cellular break-in. At this site, a carbohydrate molecule — made of different sugars — sits on the virus’s protein shell. This spot where Zika differs, called a glycosylation site, actually protrudes from the shell of the virus. In other viruses, similar protrusions act like strangers offering candy, tricking the human cell into binding with the invader. Like other flaviviruses, Zika seems to have a unique smattering of amino acids around that area.

The Food and Drug Administration has also been aggressive about trying to green-light other things that may be useful to the Zika fight. In May, it granted approval for emergency use of a Zika test from Altona Diagnostics. Another company, Hologic, said its product — a diagnostic test used to identify snippets of the Zika virus in human blood — had received similar approval to be used in emergency cases in all 50 U.S. states, plus Puerto Rico and territories.