NIAIDOn Saturday (September 7), the World Health Organization noted four additional laboratory-confirmed cases of the Middle East respiratory syndrome (MERS) in Saudi Arabia, bringing the total number of infections to 114, including 54 deaths. As scientists continue to investigate the deadly coronavirus (CoV) the causes MERS, researchers from the Spanish National Center for Biotechnology (CNB) have constructed a full-length infectious cDNA clone of the MERS-CoV genome in a bacterial artificial chromosome, which they said provides “a reverse genetics system to study the molecular biology of the virus and to develop attenuated viruses as vaccine candidates.” The CNB team’s results appeared online in mBio this week (September 10).
From the cDNA clone, coronavirus expert Luis Enjuanes of CNB and his colleagues generated recombinant MERS-CoVs lacking the ability to cause disease, but capable of invading a cell and replicating their genetic material. The team then engineered one of these mutant viruses to lack the structural envelope protein gene, making it replication-competent but propagation-defective and therefore, “a safe and promising vaccine candidate to prevent MERS-CoV infection,” the authors noted in their paper.
“The injected vaccine will only replicate in a reduced number of cells and produce enough antigen to immunize the host,” Enjuanes said in a statement.
The Spanish team isn’t the only group pursuing MERS vaccines—Rockville, Maryland’s Novavax and Aurora, Colorado-based Greffex have both reported on candidates that target the CoV’s major surface spike protein. Despite these efforts, however, The Canadian Press (CP) notes that even the most promising MERS vaccine candidates would take at least five years to become market-ready. “There’s a long way to go from showing in a research laboratory that you’ve got a potential candidate vaccine to actually producing a bottle of that vaccine that is going to be used or stockpiled,” Baylor College of Medicine’s Peter Hotez told the CP.