The story so far : India has approved two more vaccines, Corbevax and Covovax, under emergency use authorization, as well as an antiviral drug, Molnupiravir to fight against COVID-19. However, India’s expanded vaccination drive from January 3 will not immediately benefit from them.
What do we know about Corbevax?
Corbevax is a protein sub-unit vaccine and co-developed by Hyderabad-based Biological E, Baylor College of Medicine in Houston, U.S., and American company Dynavax Technologies. A protein sub-unit vaccine is made by isolating a piece of the actual virus. As fragments are used, there is no danger that these will multiply within the body. These pieces are expected to trigger an immune response that, hopefully, will stymie future infection. As only a small part of the virus –in the case of Corbevax the spike protein is the piece-- is exposed to the immune system, only antibodies specific to the spike protein are expected to be produced and less likely to trigger adverse reactions. This vaccine is therefore relatively safer than inactivated whole-virus in triggering side effects because many other parts of the virus may be exposed to the immune system.
Protein sub-unit vaccines are derived from a well-established technology and are the basis for existing vaccines for Hepatitis B and acellular pertussis. A downside to sub-units is that because they contain only a part of the virus they may miss certain characteristic signatures of the virus and the immune system may fail to recognise them. This problem is overcome by using an adjuvant or booster shots. Another weakness is that these vaccines don’t infect the cells (like inactivated, DNA or mRNA vaccines) and therefore doesn’t elicit the long-lasting immunity conferred by cells (or the T-cell response).
Biological E claims it will be able to produce 7.5 crore doses a month and scale up to 10 crore by February. The vaccine can be stored in ordinary refrigerators. The company expects to be a global manufacturing source and so India is expected to reserve doses as per requirement.
Who is producing Covovax?
Covovax is produced by the Serum Institute of India under licence from Novavax, a U.S.-based biotechnology company. Covovax has been approved by the World Health Organization under its Emergency Use Listing and therefore will also be available globally as part of the COVAX initiative to ensure that at least 40% of the world is vaccinated on priority.
It is very similar to protein sub-unit vaccines and differs from, say Corbevax, in how the spike protein is produced. In Corbevax, the spike protein is grown typically in yeast cells whereas in Covovax, spike proteins are grown in moth cells. A nanoparticle formula is used to make it resemble the structure of the coronavirus spike protein to stimulate the immune response. This also needs an adjuvant and booster shots. The vaccine has also been tested in children in India though results aren't available. In June, results from a Phase 3 clinical trial of Novavax enrolling 29,960 adult volunteers in the U.S. and Mexico showed that the vaccine demonstrated 90.4% efficacy in preventing symptomatic COVID-19 disease. It also showed 100% protection against moderate and severe disease.
When will Molnupiravir be used?
Molnupiravir, that was approved this month by the U.S. Food and Drugs Administration (US-FDA), on the heels of Paxlovid by Pfizer Inc., is said to be a promising drug for those with mild and moderate disease and can also be easily administered as a pill. Thirteen companies in India are set to manufacture this drug. It has been approved for use under emergency use authorisation for treating adults with COVID-19 “who have high risk of progression to disease.”
The US FDA in a recent statement said that because Molnupiravir works by introducing genetic errors into the virus, it ought to be prescribed with caution and wasn't recommended as a preventive and only in “certain adults” in whom alternative COVID-19 treatment options authorised by the FDA were not accessible or clinically appropriate. Paxlovid is yet to be approved in India.
How do these vaccines influence India's vaccination programme?
Prime Minister Narendra Modi announced on Saturday that from January 3, teenagers in the 15-17 years age group will be eligible for Covaxin. Healthcare workers, frontline workers and those above 60 with comorbidities who have already got two shots will be eligible for a third, “precaution” dose from January 10. For India's 15-17 year olds, the only option is Covaxin. So far around 14 crore doses have been administered and Bharat Biotech has produced far fewer vaccines than the original schedule. The company says it made 5-6 crore doses in November and expects to make a billion annually by next year. The “precaution” doses as of now will be the same as the previous two doses a person has been jabbed with. Given that Covishield accounts for about 90% of India's vaccination programme, most third doses will be Covishield. Covovax and Covishield (AstraZeneca) are the only vaccines tested as booster doses as part of the COV-BOOST study in the U.K. that tested combinations of seven vaccines. However, independent trials in India, testing Covaxin, are underway. India's National Technical Advisory Group of Immunisation continues to weigh evidence on the optimal combination of vaccines.