CureVac's COVID-19 mRNA vaccine protects mice against aggressive coronavirus variant

COVID-19 vaccine
CureVac's mRNA COVID-19 vaccine protected mice against the more infectious B.1.351 coronavirus variant in a challenge study. (solarseven/iStock/Getty Images Plus)(solarseven/ iStock/ Getty Images Plus)

Emerging coronavirus variants threaten the potency of existing COVID-19 vaccines, sending manufacturers of those products on a quest to develop booster shots. CureVac, which is in late-stage testing of its mRNA shot, now has mouse data showing its product could stave off one aggressive COVID variant.

The preclinical study found CureVac’s candidate, dubbed CVnCoV, protected mice against COVID-19 in a virus challenge study with the B.1.351 variant of the SARS-CoV-2 virus. The variant, first identified in South Africa, bears certain mutations that make it more contagious than the original virus.

It marks the first mouse challenge study that shows complete protection against a highly infectious form of coronavirus variant, CureVac Chief Scientific Officer Igor Splawski, Ph.D., noted in a statement. The results were published on the preprint site bioRxiv.

In collaboration with scientists at Germany’s Friedrich Loeffler Institute, CureVac tested CVnCoV in mice expressing human ACE2 protein. The novel coronavirus uses its spike protein to bind to the ACE2 protein on the surface of human cells to gain entry and spark infection.

The animals were challenged with either the original coronavirus strain or B.1.351 at high doses that could induce severe disease resembling COVID-19 in humans. Before that, some animals received two doses of CVnCoV. Control rodents either got an inactivated and adjuvanted SARS-CoV-2 virus or nothing.

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The B.1.351 variant has been linked to reduced neutralization by currently available antibody drugs and vaccines. Moderna reported a sixfold reduction in neutralizing titers for its FDA-authorized mRNA vaccine against B.1.351 versus the original virus. Pfizer and BioNTech’s FDA-authorized mRNA shot was found to provide about two-thirds lower neutralization of the variant than of an early isolate of SARS-CoV-2.

Although the CureVac vaccine elicited strong antibody responses in mice, neutralization titers against B.1.351 were also significantly reduced compared with the ancestry strain, the new study found.

Nevertheless, mice that were immunized with CVnCoV were completely protected from both B.1.351 and the original virus, as all animals were alive after the virus challenge with no significant weight loss or disease symptoms throughout the course of the study. In comparison, mice that got the control immunization showed weight loss and viral symptoms, the researchers reported.

What’s more, no viral genome was detected in oral swabs from the CVnCoV-vaccinated animals in the challenge groups. The vaccine also blocked viral replication of B.1.351 in the lower respiratory tract and the brain, and it reduced viral levels in the upper respiratory tract.

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CureVac moved CVnCoV into a pivotal phase 2b/3 study called HERALD in December after showing in a phase 1 trial the mRNA vaccine could elicit a strong immune response that was comparable to that seen in recovered COVID-19 patients.

As new coronavirus variants start to gain footholds in different parts of the world, CureVac on Monday said it will expand the pivotal trial in Europe and Latin America so it can separately analyze its vaccine’s efficacy against select variants. The German biotech still expects to have data available by the end of June.

Meanwhile, the company recently teamed with GlaxoSmithKline to develop a next-generation, multivalent mRNA COVID vaccine to target emerging variants. It also has a deal with the U.K. government to study multiple variants and develop vaccines against them.