The researchers say the MERS-CoV candidate vaccine has passed all the preclinical tests and is ready to start human trials.
Image credit: Gerd Sutter/LMU
The news follows a study led by Ludwig-Maximilians-Universität München in Germany (LMU) that demonstrated the vaccine's protective effect in the lab and in mice.
Writing in the Journal of Virology, the researchers conclude that the vaccine - called MVA-MERS-S - meets important criteria for use in human trials.
At first, infection causes flu-like symptoms, but they can progress to a severe respiratory illness that can be fatal.
There is currently no vaccine against MERS-CoV, which kills around 36% of people it infects.
MERS-CoV was first identified in 2012 when it emerged in Saudi Arabia. It has spread to other countries in the Arabian Peninsula and beyond, including the US and Germany - where the vaccine has been developed.
The present MERS outbreak in South Korea - where 166 confirmed cases and 12 deaths have been reported - is the largest so far recorded outside the Middle East.
Vaccine based on a safe virus carrying MERS-CoV antigen
Two years ago, Gerd Sutter, a virology professor and chair of LMU's Institute for Infectious Diseases and Zoonoses, and his team reported they had developed a candidate vaccine against MERS-CoV.
As well as researchers from LMU, the vaccine development team includes members from Marburg University in Germany, and the Erasmus Medical Center of Rotterdam in the Netherlands.
In the new study, they describe how subsequent preclinical tests confirm that the vaccine is effective, paving the way for phase 1 trials in humans.
The idea of a vaccine is to prime the immune system to fight a particular disease without causing the subject to actually have the full-blown disease.
In this study, the team based the candidate vaccine on a safety-tested vaccine virus called Modified Vaccinia virus Ankara (MVA).
They used MVA as a vehicle to carry an MERS-CoV antigen called the spike glycoprotein (protein S). An antigen is a part of a virus, bacteria, or other unwanted material that causes the immune system to produce antibodies to eliminate it.
Once inside the body, the modified virus gets into cells and makes many copies of the MERS-CoV protein S, displaying them on the cell surface so they can be readily recognized by the immune system.
When the immune system recognizes the MERS-CoV protein S, it begins to produce antibodies and T cells against the pathogen.
Tests in cell cultures and mice showed vaccine is effective
As a first step, the researchers showed the vaccine had the desired immune reaction in cell cultures - it produced protective levels of MERS-CoV-neutralizing antibodies.
Next, the team used mice genetically modified to be susceptible to MERS-CoV infection and exposed them to varying doses of the vaccine.
Tests showed the MERS virus could not replicate itself in mice that had received the highest doses of vaccine. They also showed the vaccinated mice had lower levels of MERS DNA in their lungs than non-vaccinated mice.
Prof. Sutter says the results show the vaccine candidate is both safe and effective, and:
"Thus, there is no obvious risk that the resulting immune response might exacerbate rather than prevent the infection."
Planning for the next step, a phase 1 clinical trial in humans, is already under way with the help of a €1.5 million ($1.66 million) grant from the German Center for Infection Research (DIFZ).
Meanwhile, Medical News Today recently covered a report of Thailand's first confirmed case of MERS. Public health minister Rajata Rajatanavin said a man who traveled to Thailand from the Middle East has tested positive for the virus.