New MERS vaccine may block coronavirus infections, study shows

A novel vaccine fully protects mice against a lethal dose of MERS, a close cousin of the novel coronavirus that causes COVID-19, scientists said on Tuesday.

The vaccine uses a harmless virus to deliver a MERS coronavirus protein into cells to generate an immune response, said the researchers from researchers at the University of Iowa and the University of Georgia in the US.

It may hold promise for developing vaccines against other coronaviruses diseases, including COVID-19, they said.

The team tested the MERS vaccine candidate in mice engineered to be susceptible to the MERS coronavirus.

The vaccine is an innocuous parainfluenza virus (PIV5) carrying the "spike" protein that MERS uses to infect cells. All the vaccinated mice survived a lethal dose of the MERS coronavirus, according to the results published in the journal mBio.

"Our new study indicates that PIV5 may be a useful vaccine platform for emerging coronavirus diseases, including SARS-CoV-2, the virus causing the ongoing COVID-19 pandemic," said Paul McCray, a professor the University of Iowa.

"Using the same strategy, vaccine candidates based on PIV5 expressing the spike protein of SARS-CoV-2 have been generated, McCray said.

The researchers are planning more studies in animals to test the ability of PIV5-based vaccines in preventing disease caused by SARS-CoV-2.

MERS (Middle East Respiratory Syndrome) and COVID-19 are both caused by coronaviruses.

MERS is deadlier and is fatal in about one third of known cases, but there have been only 2,494 cases since 2012, when the virus first emerged, the researchers said.

In contrast, there have been over 1.25 million confirmed cases of COVID-19 worldwide since it first emerged in late 2019 in Wuhan, China, and almost 70,000 people have died from the disease, they said.

The study found that just one, relatively low dose of the vaccine given to the mice intranasally -- inhaled through the nose -- was sufficient to fully protect all the treated mice from a lethal dose of MERS coronavirus.

When the researchers analysed the immune responses generated by the vaccine, they found that both antibodies and protective T cells were produced.

However, the antibody response was quite weak and it seems most likely that the vaccine's protective effect is due to the T cell response in the mouse lungs.

The researchers note several factors that make PIV5 expressing a coronavirus spike protein an appealing platform for vaccine development against emerging coronaviruses.

PIV5 can infect many different mammals, including humans, without causing disease, the researchers said.

The fact that a low dose of the vaccine was sufficient to protect the mice might be beneficial for creating enough vaccine for mass immunization, the researchers said.

Also, the vaccine in the current study was the most effective MERS vaccine to date in animal models of the disease, they said.