India's Covid-19 vaccination drive will soon include two new candidates for the under-18 age group as the DCGI gave its nod to Biological E's Corbevax for emergency use in the 5-12 age group, and the Standing Technical Sub-Committee of the NTAGI has recommended inclusion of the Serum Institute's Covovax in the national vaccination drive for the 12-17 age group.
The vaccines will join Bharat Biotech's Covaxin, which is currently available for inoculation of the 12-18 age group and has been given EUA for the 6-12 age group, and Zydus Cadila’s ZyCoV-D vaccine which has been approved for the 12-plus age group, expanding the scope of India's vaccination drive.
How are Corbevax and Covovax different?
Corbevax is a recombinant protein subunit vaccine, meaning it is made up of a specific part of SARS-CoV-2 virus which causes Covid-19 - the spike protein on the virus’s surface. It is developed by the Texas Children's Hospital Center for Vaccine Development and Baylor College of Medicine and licenced to India's Biological E.
On the other hand, Covovax is described as a recombinant nanoparticle vaccine by its developer Novavax.
How is a recombinant protein subunit vaccine different from a recombinant nanoparticle vaccine?
In a typical viral infection scenario, the spike protein allows a virus to enter cells so that it can replicate and cause disease in its host.
In a recombinant protein subunit vaccine, the spike protein is injected into the body, however, it is not as harmful as the virus itself, because only this spike protein is injected and the rest of the virus is missing. The idea is that when the real virus enters the host's body, the host will already have an immune response ready and thus not fall seriously ill. This platform is already in use in hepatitis B vaccines.
A recombinant nanoparticle vaccine, on the other hand, mimics this spike protein and creates a mechanism where your body can identify the target spike protein and generate an immune response. Here the body is exposed to a simulated spike protein to generate that reponse as opposed to injecting the virus itself.
"Novavax makes a protein that precisely mimics the virus’ version of the spike protein. In our vaccine, we organise spike proteins into a nanoparticle to help your immune system recognize the target spike. Learning to recognize the spike proteins in this way helps your immune system protect you from getting sick from Covid-19," Novovax explains on its website.
However, to trigger the immune response to this nanoparticle, a Matrix-M 'adjuvant' is required. "Tiny Matrix-M adjuvant particles increase the activity of your immune system when you receive a vaccine.Together, the vaccine’s spike protein and Matrix-M adjuvant help stimulate a protective immune response," the company said.
The Covovax vaccine is produced by creating an engineered insect virus called baculovirus containing a gene for a modified SARS-CoV-2 spike protein, which is then used to infect moth cells, creating the spike protein on the cell embrane. The protein is then harvested and assembled into the vaccine.
How are Corbevax and Covovax administered? And how many doses?
Both vaccines, like the existing jabs such as Covishield, Covaxin and ZyCoV-D, are administered via an injection. However, unlike ZyCoV-D, which uses an intradermal delivery system, which is to say the vaccine is injected only into the middle layer of the skin, the dermis, Corbevax and Covovax use an intramuscular delivery system like Covishield and Covaxin, in which the vaccine is administered into muscle tissue.
Both Corbevax and Covovax will be administered as a two-dose regimen.
How do the vaccines differ from Covishield and Covaxin?
Covishield is a viral vector vaccine developed by AstraZeneca, which uses a weakened chimpanzee adenovirus that causes common cold, genetically engineered to produce coronavirus proteins in the body. However, the virus is weakened and cannot cause the disease in the host.
As of 2021, only six vaccines use the viral vector delivery method in the world - four Covid-19 vaccines including Covishield and Sputnik V - and two ebola vaccines.
On the other hand, Covaxin uses the entire SARS-CoV-2 virus in inactivated form, making it a more traditionally-developed vaccine. As the name suggests, in an inactivated vaccine, the pathogen for the disease is put in a culture and then killed to reduce infectivity but trigger an immune response nonetheless.
Initially developed in the late 19th century for cholera and typhoid, inactivated vaccines are among the most widely-used delivery platforms, covering a host of diseases like influenza, polio and, hepatitis A and rabies.
Which countries have authorised Corbevax and Covovax?
As of 2022, four countries allow use of Corbevax. While India has given it emergency use authorisation, New Zealand, Turkey and Malaysia have approved it as a valid vaccine for incoming travellers. On the other hand, Novavax's vaccine is authorised in 51 countries along with a World Health Organization authorisation. Four countries - Australia, Canada, Japan and South Korea - have given it full authorisation, while 37 countries including India have given it emergency use authorisation. 10 countries, including Hong Kong and Palau allow it for incoming travellers.
How much do these two vaccines cost?
Corbevax costs Rs 990 including taxes per dose, and is available for free in government-run vaccination centres. Meanwhile, Serum Insitute of India wants to charge private hospitals Rs 900 per dose plus GST for a dose of Covovax, but has not provided any price estimates for government hospitals.
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