New COVID-19 vaccine elicits strong protective immunity in mice and monkeys

Researchers have developed a new COVID-19 vaccine that has proven safe and effective in mice and monkeys. The study was conducted at the Yerkes National Primate Research Center, Emory University, US. 

The vaccine induces protective immunity via modified vaccinia Ankara (MVA), a harmless version of a poxvirus. The researchers report that the Emory MVA COVID-19 vaccine induces strong neutralising antibodies, which support the immune system’s ability to fight infections. It induces killer CD8 T cells in addition to the neutralising antibodies, providing a multi-pronged approach to halting SARS-CoV-2. The researchers say the vaccine is easily adaptable to address disease variants, can be used in combination with existing vaccines to improve their ability to combat variants and has the potential to be equally effective with a single dose.

The team tested two MVA SARS-CoV-2 vaccines in mice. One of them, MVA/S, used the complete Spike (S) protein of coronavirus to induce strong neutralising antibodies against SARS-CoV-2. In addition, this vaccine also induced a strong killer CD8 T-cell response.

“Generating neutralising antibodies is an important component of a successful COVID-19 vaccine because the antibodies can block the virus from entering the body’s cells. It is as important to activate CD8 T cells that can clear infected cells, so this allows us to approach halting the virus two ways simultaneously. The CD8 T cells also provide ongoing value because they are key to working against other variants of the virus, especially if antibodies fail,” said Dr Rama Amara, lead researcher of the study. 

Based on the encouraging study results in mice, the team advanced the MVA/S COVID-19 vaccine into a study with 10 rhesus monkeys. For five animals, the researchers gave two doses of the vaccine a month apart and then challenged them with SARS-CoV-2. The researchers also challenged a group of five monkeys that received a placebo MVA vaccine, which did not contain any genes from the COVID-19 virus. The virus grew to high levels in the lungs of all five placebo animals by the second day, but was below detection limits in all five MVA/S-vaccinated animals.

“Comparing the virus in vaccine and placebo groups provided clear results the MVA/S vaccine is safe and effective against SARS-CoV-2,” said Amara. “These results are even more promising because the MVA/S-vaccinated animals did not show any signs of inflammation in the lungs such as what medical professional are seeing in humans who have COVID-19.”

Amara will continue his work on COVID-19 vaccines. One study will focus on the effectiveness of a single dose of the Emory MVA COVID-19 vaccine. In a second study, Amara’s team will focus on inducing broader T-cell responses capable of fighting new COVID-19 variants and other human coronaviruses.

“The newly designed vaccines aim to induce T cells against multiple other genes of the virus in addition to targeting the S protein,” said Amara. “This requires inserting multiple genes of the coronavirus into the vaccine, which can be challenging. MVA, however, is well-suited for this because of its unique capacity to carry extra genes.”

The results are published in Immunity.