Measles vaccine used as base for experimental COVID vaccine

Colorized scanning electron micrograph of a cell (teal) infected with SARS-CoV-2 virus particles (orange), isolated from a patient sample. NIAID Integrated Research Facility

The measles vaccine is one of the safest and most effective vaccines. Introduced in the 1960s, it has been shown to be safe in both children and adults, providing long-term protection against the measles virus. The vaccine uses a live but weakened strain of the measles virus.

Because of that vaccine’s proven track record, researchers used it to develop an experimental vaccine against SARS-CoV-2, the virus that causes COVID-19. A research team led by Dr. Jianrong Li of Ohio State University created and tested a series of measles-based vaccine candidates. They developed the vaccines by inserting genes for different forms of the coronavirus spike protein into the measles vaccine genome. SARS-CoV-2 uses its spike protein to enter and infect cells.

The modified measles virus acts as a vehicle to carry the gene for the spike protein into the body. This gene instructs cells in the body to produce the coronavirus spike protein, prompting the immune system to produce antibodies that recognize the protein. This trains the immune system to neutralize the virus if it’s encountered.

The study was funded in part by NIH’s National Institute of Allergy and Infectious Diseases (NIAID), National Human Genome Research Institute (NHGRI), and National Cancer Institute (NCI). Results appeared on March 23, 2021, in the Proceedings of the National Academy of Sciences.

The team identified the most promising vaccine candidate, which produced the highest levels of neutralizing antibodies against SARS-CoV-2 in rodents. The vaccine carried the gene for the stabilized “prefusion” version of the spike protein—the protein’s shape before it infects a cell. The prefusion spike protein structure is the basis for the currently available vaccines. This includes the mRNA vaccines made by Moderna and Pfizer-BioNTech.

Experiments showed that the new vaccine, called rMeV-preS, produced levels of neutralizing antibodies in rodents higher than those found in recovered COVID-19 patients. The vaccine also produced a strong T cell response. T cells are immune cells that fight infection and are an important measure of vaccine effectiveness.

The team then tested whether the vaccine would protect against SARS-CoV-2 infection. Using golden Syrian hamsters, which can contract COVID-19, they found that rMeV-preS protected the hamsters from infection. It even prevented the virus from replicating in the lungs and nasal passages.

These findings show promise for rMeV-preS. While multiple COVID vaccines are now available to the public, this new candidate may offer advantages. The measles vaccine has already been established as safe, effective, and long-lasting. Several experimental measles-based vaccines against other viruses are now being tested in clinical trials. The new vaccine could protect jointly against COVID-19 and measles.

"We don't yet know how long the mRNA vaccines will protect or how much they will cost. In the meantime, an alternative vaccine that should protect for a long time, is easy to manufacture, and cheap seems like a good idea,” says co-author Dr. Stefan Niewiesk of Ohio State University.

—by Erin Bryant