Scientists in the US have developed a new COVID-19 vaccine that offers superior immune protection against two viral subvariants of Omicron than standard mRNA shots.

The vaccine, called Omnivax, increased neutralising antibody response against the BA.1 and BA.2.12.1 Omicron subvariants in pre-immunised an experimental model 19-fold and eight-fold, respectively, compared with standard mRNA vaccines.

The improved response against the BA.1 subvariant was reported on June 6 in the journal Nature Communications. The results of the study involving the BA.2 subvariant were published July 19 in the journal Cell Discovery.

"While standard mRNA vaccines still offer protection against infection from new variants, their effectiveness wanes over time and was compromised due to immune escaping mutations in emerging variants," said Sidi Chen, an associate professor at Yale University, US, and senior author of both studies.

"We wanted to see if we could develop variant-specific vaccines that offer additional protection against emerging subvariants," said Chen.

The experimental vaccines, developed in Chen's lab by a team headed by postdoctoral associate Zhenhao Fang, use engineered lipid nanoparticles to deliver mRNA to cells with "instructions" to create spike proteins from mutating variants, which the virus uses to attach to and infect cells.

The presence of these foreign viral fragments prompts the immune system to create antibodies against the virus. The rapid mutation of spike proteins on the surface of the virus over time has created a parade of subvariants and enabled them to blunt the protection of earlier generations of mRNA vaccines developed by Moderna and Pfizer-BioNTech.

The engineered lipid nanoparticle mRNA vaccines can be created quickly, the researchers said. The BA.1 subvariant emerged in mid-November, and by mid-December, the researchers had developed a vaccine against the new strain. However, testing the efficacy of the vaccine in an experimental model and a peer review of the study were not completed until February.

By March, the BA.2 subvariant had taken hold as the predominately circulating strain throughout most of the world. The researchers then investigated whether the Omicron variant vaccine maintains its superiority over standard vaccines against BA.2. The new vaccine also boosted an immune response superior to standard vaccines in an experimental model against this subvariant, researchers said.

"Although translating the new vaccine candidate from bench to bedside requires rigorous testing in human trials, these preclinical studies provide a comprehensive and unbiased evaluation of an Omicron-specific vaccine candidate, which will hopefully fuel the development of next-generation COVID vaccines," Chen said.

In light of the rise of new BA.4 and BA.5 variants, which have become most common among COVID cases, the researchers are currently testing a new vaccine candidate against these variants in an experimental model.

"We have a system in place to combat these emerging subvariants, but we need to adjust the system to respond more quickly to emerging health threats," Chen added.