India has placed an advance order to block 300 million doses of a new Covid-19 vaccine, Corbevax.
- Corbevax is Covid-19 vaccine, from Hyderabad-based company Biological E.
- Corbevax is a ‘Recombinant protein subunit’, also known as a ‘receptorbinding domain’ (RBD) vaccine.
- It is India’s indigenous Covid-19 vaccine which is currently undergoing Phase 3 clinical trials.
- It has a schedule of two doses administered via intramuscular injection 28 days apart. It can be stored in an ordinary refrigerator.
- It is made using a low-cost platform
How Corbevax works
Corbevax is a “recombinant protein sub-unit” vaccine, which means it is made up of a specific part of SARS-CoV-2 — the spike protein on the virus’s surface. The spike protein allows the virus to enter the cells in the body so that it can replicate and cause disease. However, when this protein alone is given to the body, it is not expected to be harmful as the rest of the virus is absent. The body is expected to develop an immune response against the injected spike protein. Therefore, when the real virus attempts to infect the body, it will already have an immune response ready that will make it unlikely for the person to fall severely ill. Corbevax will be among the first Covid-19 vaccines to use this platform
- hepatitis B vaccines made from the same technique
- Novavax has also developed a protein-based vaccine, which is still waiting for emergency use authorisation from various regulators.
How Corbevax is different
- Other Covid-19 vaccines approved so far are either mRNA vaccines (Pfizer and Moderna), viral vector vaccines (AstraZeneca-Oxford/Covishield, Johnson & Johnson and Sputnik V) or inactivated vaccines (Covaxin, Sinovac-CoronaVac and Sinopharm’s SARS-CoV-2 Vaccine–Vero Cell).
- Inactivated vaccines, which include killed particles of the whole SARS-CoV-2 virus, attempt to target the entire structure of the virus. On the other hand, Corbevax, like the mRNA and viral vector Covid-19 vaccines, targets only the spike protein, but in a different way.
- Viral vector and mRNA and vaccines use a code to induce our cells to make the spike proteins against which the body have to build immunity
Recombinant protein subunit RBD vaccine
The coronavirus uses its spikes to attach to human cells. Within a spike, a part called ‘receptor binding domain’ or RBD lets it dock with and infect cells. An RBD subunit vaccine like Corbevax contains only the virus’s RBD proteins. Different protein subunit vaccines may use different parts of the virus.
- Advantages of Protein subunit vaccines
- Instead of the whole virus, they contain only the components that best stimulate the immune system.
- Including only some specifi c parts of a virus minimises side effects, and the vaccines are easier to make
- These vaccines are similarly effective as whole-cell vaccines but much less likely to cause adverse reactions,” says America’s National Institute of Allergy and Infectious Diseases
- As these vaccines cannot cause disease themselves, they are also suitable for people with compromised immune systems
- Another big advantage of using specifi c virus proteins is that these vaccines can be more stable than those containing whole viruses
- Because the immune system is exposed to only a few virus parts, it may not respond strongly to the vaccine.
- Also, the resulting immunity may be limited to antibodies that wane with time.
- To overcome this weakness, protein subunit vaccines usually contain another substance, called adjuvant, to stimulate the immune system strongly. Corbevax uses the adjuvant. ‘CpG 1018’ made by US-based Dynavax