EXPLAINED: Biological E’s Corbevax Cleared For Emergency Use, Know How The RBD Protein Sub-Unit Vaccine Works

Corbevax is India’s first indigenously developed receptor-binding domain (RBD) protein sub-unit vaccine against Covid-19, manufactured by Hyderabad-based firm Biological E.

Representational image of a Covid-19 vaccine | Photo: Getty

New Delhi: The Ministry of Health and Family Welfare Tuesday granted emergency use authorisation (EUA) to the Serum Institute of India’s (SII) Covovax, and Biological E's vaccine Corbevax, with certain conditions, after a recommendation from the Central Drugs Standard Control Organisation's expert panel.

Union Health Minister Dr Mansukh Mandaviya made the announcement on Twitter. He posted: “CORBEVAX vaccine is India's 1st indigenously developed RBD protein sub-unit vaccine against #COVID19, Made by Hyderabad-based firm Biological-E. It's a hat-trick! It's now 3rd vaccine developed in India!”

While the SII’s Covovax is a nanoparticle-based vaccine, Hyderabad-based firm Biological E’s Corbevax is an RBD protein subunit vaccine.

CORBEVAX is India’s first indigenously developed receptor-binding domain (RBD) protein sub-unit vaccine against Covid-19. The RBD is a part of the spike protein of SARS-CoV-2. The virus uses the spike protein to attach itself to host cells.

What Is An RBD Protein Sub-Unit Vaccine?

Sub-unit vaccines, also called acellular vaccines, contain purified pieces of a pathogen, which have been specifically selected for their ability to stimulate immune cells, according to an article published by Gavi, the Vaccine Alliance — a public-private global health partnership that helps vaccinate almost half of the world’s children against deadly and debilitating infectious diseases.

Sub-unit vaccines are of different types, and are considered safe because the purified fragments are incapable of causing disease. They include only the parts of a virus that best stimulate one’s immune system, according to a Mayo Clinic article.

Protein sub-unit vaccines contain specific isolated proteins from viral or bacterial pathogens, and are being developed against SARS-CoV-2. Hepatitis B vaccines are other examples of protein sub-unit vaccines. An RBD protein sub-unit vaccine against Covid-19 makes use of a specific part of SARS-CoV-2 ­— the spike protein. It is a recombinant vaccine, which means it is manufactured using living organisms such as yeast cells.

RBD protein sub-unit vaccines are suitable for people with compromised immune systems, consist of no live components, as a result of which there is no risk of the vaccine triggering disease, and are relatively stable. However, they are more complex to manufacture, compared to other Covid-19 vaccines, and adjuvants and booster shots may be required after receiving the primary vaccination doses. 

How Does An RBD Protein Sub-Unit Vaccine Work?

An RBD protein sub-unit vaccine is one which induces protective immunity by targeting the RBD of the S protein of SARS-CoV-2, which is a harmless protein. The vaccine comprises residues of the RBD protein, according to a study published in the journal, Nature.

The residues of the RBD protein used in the vaccine are carefully studies to identify which combinations of the molecules are likely to produce a strong and effective immune response, according to the Gavi article. The body develops an immune response against the injected fragments of the spike protein.

The immune system recognises the S proteins, and creates antibodies and defensive white blood cells. If the person becomes infected with the Covid-19 virus in future, the antibodies will fight the virus.

An RBD protein sub-unit vaccine, like Corbebax, helps the immune system recognise the S proteins, and create antibodies.