On November 20, Inovio Pharmaceuticals, Inc. reported positive results in preclinical trials of the first DNA synthetic vaccine against the Middle East Respiratory Syndrome Coronavirus (MERS-CoV), an emerging disease that has so far killed 42 percent of known cases.

Inovio’s vaccine is a DNA synthetic vaccine, which refers to how the vaccine is developed and produced. Whereas previous vaccine technology used a whole or part of a pathogen (virus, bacteria, or bacterial toxin), DNA vaccines work by using DNA (short for deoxyribonucleic acid — basically meaning genetic information) from a pathogen to elicit an immune response in a host– ideally, in humans. The vaccine delivers the pathogen’s foreign genes into a host cell, mimicking natural infection. The immune system then responds as it normally would to an infected cell. However that infected cell is not truly infected; the virus is not alive, cannot replicate, and cannot spread in the host. DNA vaccines are thought to have advantages in effectiveness, safety, and cost when compared to other vaccines.

What lies ahead for Inovio’s MERS-CoV vaccine candidate? Vaccine development is a long process with careful testing at every step. Inovio reported results from pre-clinical animal testing. In this stage, researchers use cells, tissues, and animals to test a vaccine candidate for safety and the ability to provoke an immune response (known by the tongue-twister “immunogenicity”). Many vaccine candidates never make it past this stage, which can last three to six years.

For promising candidates, the next step in the process is a series of clinical trials to assess the safety in humans and to determine what kind of immune response is produced. During three phases of clinical trials, the vaccine candidate is first tested on a small group of adults in a Phase I trial, typically no more than 10-12 people. With positive results, researchers move on to randomized controlled trials involving first several hundred (Phase II) and then thousands to tens of thousands individuals (Phase III). A randomized controlled trial (RCT) is a type of experiment where participants are randomly assigned to one of two groups: a treatment group (here, those receiving the vaccine candidate), and a control group receiving a placebo. By comparing the two groups, researchers can zero in on the real effects of the vaccine candidate and statistically rule out effects or side effects that are likely due to chance or coincidence.

If a vaccine candidate completes all of the above stages and is approved by the Food and Drug Administration (FDA), it can enter the U.S. market. There are post-marketing surveillance systems to monitor safety and efficacy, including optional Phase IV trials conducted by the manufacturer and the Vaccine Adverse Event Reporting System (VAERS), a voluntary reporting system managed by the Centers for Disease Control and Prevention (CDC) and the FDA.

In September, a group of scientists in Madrid, Spain reported that they had genetically engineered a weakened strain of the MERS-CoV virus that could be used to create a vaccine, so there are multiple possibilities for a vaccine in the future.

The MERS-CoV outbreak started in September 2012, when a Qatari man was admitted to a hospital in Doha with respiratory problems and kidney failure. Since then, the WHO has received reports of 157 laboratory-confirmed cases and 66 deaths. The majority of cases and deaths have been in Saudi Arabia, where the virus has sickened 129 people and resulted in 54 deaths. The primary symptom of MERS-CoV is respiratory disease. Diarrhea is also common, and severe complications include renal failure and acute respiratory distress syndrome (ARDS) with shock.

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