2 min read.Updated: 30 Dec 2021, 11:12 PM ISTDIVYA RAJAGOPAL
India now has one of the largest baskets of covid-19 vaccines in the world. Earlier this week, the country approved two new vaccine candidates, taking the total to eight. Mint explains how the new vaccines work:
How do Covovax and Corbevax work?
Both are based on the second-generation platform known as protein vaccines that are safer than the traditional platforms such as the inactivated whole-cell ones. Protein-based vaccines are built using specific particles of a virus that have the ability to generate an immune response, known as anti-gens. The antigens are combined with an ‘adjuvant’ to trigger the immune response. In Covovax, a plant-based adjuvant known as saponin is combined with the protein of the first strain of SARS-CoV-2. Corbevax uses particles from the receptor-binding domain of the virus’ spike protein to trigger an immune response.
What is the dosage recommended?
Both are approved as two-dose vaccines within a span of one month. These vaccines are not yet recommended for children. The World Health Organisation (WHO) has recommended a third dose of Covavax for immunocompromised people and also recommends its use in pregnant women. WHO’s scientific advisory group for vaccine effectiveness has noted that though there is no data for Covavax on pregnant women, the past experience of using the protein-based vaccine has been safe. Data for Corbevax is currently available only for adults. Detailed guidelines are awaited. However, the firm has started a booster trial in India.
What are the benefits of protein-based jabs?
They tend to be safer as they do not use live or weakened virus particles that could lead to vaccine-induced infection. This platform dominates several new generation vaccines such as Hepatitis B and HPV vaccines. The high safety profile makes them suitable for immunocompromised people. But they may not trigger a lasting immune response. Boosters are therefore required.
Do these vaccines work against variants?
Novavax (one of the firms behind Covavax) said the third dose of the vaccine produced an increased immune response against Omicron and also provided cross reactive immune response against variants such as Delta. It is now developing an Omicron-specific jab, expected to go into production by January 2022. Corbevax doesn’t have the data yet on Omicron effectiveness, but it triggers a better immune response against Delta compared to Covishield, with over 80% efficacy against symptomatic infection.
Though the two jabs have received emergency use authorization, there is no announcement from the government on whether it will buy the vaccines to be used in the immunization programme. The companies have not made any announcements on whether they will sell these vaccines in the private market. However, as the government has announced boosters for front-line workers and those above 60 who are immunocompromised, these vaccines could become possible booster shots.
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