Use of live virus to block coronavirus infection

Before getting contained MERS (Middle East respiratory syndrome) spread to 27 countries in the year 2012, infecting 2494 people and causing 858 deaths with a high fatality rate of 34%. 

According to an article published in mBio, a journal of the American Society of Microbiology, scientists may have found a way to form a vaccine for MERS which can also work for the novel coronavirus, SARS-CoV-2. The vaccine is actually a live RNA virus called parainfluenza virus 5 (PIV5). 

Parainfluenza virus is identified as a cause for an infectious condition in dogs known as kennel cough. However, PIV5 seems to be an innocuous virus in humans and does not cause a cytopathic effect (does not change healthy cells into virus cells). The researchers further added an extra gene to the parainfluenza virus which stimulates the infected cells to produce the S/spike glycoprotein which helps in mediating the entry of the MERS virus.

The study was led by Paul McCray, a scientist from the University of Iowa along with a virologist, Biao He, from the University of Georgia. The study was done over a bunch of mice who were infected with the MERS virus. Since MERS virus cannot replicate in mice, Dr McCray genetically engineered the mice with a protein, DPP4, which allows the entry of MERS virus in the human cells.

The PIV5 vaccine was given in three different forms: intranasally with S glycoprotein, intranasally without S glycoprotein and intramuscular vaccine with inactivated MERS virus. 

The vaccine was given for four weeks and then the mice were exposed to a strain of MERS virus which could cause lethal infection in them. 

The scientists stated that after they delivered the first intranasal dose in the mice, the vaccine effectively stimulated the infected cells to produce the S glycoprotein. Since the S glycoprotein is the main target of the humoral immune response, the immune responses activated against the protein in the animal host.

The lab reports of the mice four weeks after they received the vaccine showed that all the mice who were immunized with the S glycoprotein containing PIV5 virus survived the MERS virus infection. 

However, the mice who were immunized with the PIV5 without S glycoprotein died due to the infection. 

Amongst the third group of mice who received the intramuscular dose of vaccine containing inactivated MERS virus, only 25% managed to survive from the lethal infection. They showed increased levels of eosinophils and white blood cells which indicate inflammation in the body. 

The scientists concluded that an intranasal dose of PIV5-based vaccine is most effective against MERS in mice. They are yet to test the vaccine on humans but are optimistic about the effectiveness of the vaccine.

Scientists are hopeful that by using live viruses as a delivery vehicle for the vaccines, they would be able to find a cure for various diseases including cystic fibrosis. 

Both Dr McCray and Dr He have focused their efforts and research work in making mouse models for testing and finding a vaccine or a cure for the SARS-CoV-2 virus. They want to make a vaccine for this infectious disease as there is no proof which would determine that people who have been infected with the COVID-19 infection would develop lasting immunity from the SARS-CoV-2 virus.