Study Finds New Zika Vaccine Candidate That Protects Against The Infection With A Single Dose

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A recent study by researchers at Perelman School of Medicine at the University of Pennsylvania discovered a new Zika vaccine candidate that has the potential to protect against the virus with a single dose. The researchers reported that the preclinical tests displayed promising immune responses in monkeys and mice.

"We observed rapid and durable protective immunity without adverse events, and so we think this candidate vaccine represents a promising strategy for the global fight against Zika virus," senior author and professor of Infectious Disease at Penn, Drew Weissman, MD, PhD, said. The researchers collaborated with several other laboratories including Theodore C. Pierson at the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH) and the laboratories of Barton F. Haynes at Duke University.

Their study was inspired by the current outbreaks in Latin America which has put scientists in some parts of the United States and around the world in a struggle to develop candidate vaccines with many already tested in animals. The newly found candidate vaccine is the first to display a long-lasting effect without the use of a live virus, according to Science Daily.

The traditional viral vaccines comprises of a weakened or dead version of the isolated viral proteins, in contrast with the new Zika candidate vaccine that utilizes small strands of RNA which hold the genetic codes for making viral proteins. The RNA molecules are the modified versions of the messenger RNAs (mRNAs) produced and purified in a laboratory and administered like a normal vaccine in an injection.

Typically, the mRNAs would be cleared from the body by the immune system few minutes after injecting with the vaccine, but these mRNAs would be ignored by the immune system because they are modified, thus, allowing them to penetrate cells easily. They are taken up by cellular protein-making machinery once they inside the cells, where they induce the production of the viral proteins they encode, over weeks.

The researchers report that the new candidate vaccine contains mRNAs encoding two key proteins from a Zika virus strain isolated back in 2013. They discovered that a single injection of 30 millionths of a gram of the mRNAs in mice induced an immune response that protected them from intravenous exposure to a separate Zika strain after two weeks. The protection which resulted in zero detectable virus in the bloodstream few days after exposure, was maintained five months later when the mice were exposed to Zika virus.

The tests in macaques also revealed that a single 50 micrograms dose of the vaccine provides a strong protection against exposure to Zika virus five weeks later. Virus neutralization tests in both cases showed that the vaccine induced high levels of antibodies that blocked the infection with the levels reaching their peak (Up to 25 times greater) after several weeks and remained high enough to be protective thereafter, potentially for years.

The powerful protection offered by the candidate vaccine is partly due to its strong stimulation of CD4 helper T cells necessary for maintaining long-term antibody immunity. Since the vaccine is effective after just a single immunization the researchers believe that the infrastructure necessary for its administration would be much simpler, according to Medical Express.

Also, the production of an mRNA-based vaccine will possibly be easier and less expensive than traditional viral protein-based vaccines. The researchers revealed that they hope to start clinical trials in 12 to 18 months. They published their findings in Nature.