Covid-19: Why technical advisory panel wants booster dose to be different than first two vaccines

A Covid-19 booster dose, when administered, should be of a vaccine based on a different platform than the first two doses, according to preliminary consensus reached by India’s top technical advisory body on the pandemic, The Indian Express reported.

The final decision on recommending a booster shot, however, is still to be taken. Government sources told The Indian Express that the National Technical Advisory Group on Immunisation was still assessing the requirement for boosters.

However, there is a general agreement that the third dose for a beneficiary who has been vaccinated with an inactivated-whole virus or adenoviral vector shot should be of a vaccine based on a different platform.

Covaxin, manufactured by Bharat Biotech, is an inactivated virus vaccine, while the Russia-made Sputnik V and Serum Institute of India’s Covishield are adenovirus-based vaccines.

A senior official told The Indian Express that the preliminary consensus was that a beneficiary could not take three doses of Covishield or Covaxin.

The source said this also meant that the third dose for a fully-vaccinated individual who had taken both does of Covishield could not be Covaxin and vice versa. The same would also apply to Sputnik V.

Viral vector vaccines such as Sputnik V and Covishield use a modified version of a virus, different from the one being targeted to deliver instructions to the recipient’s cells. The virus altering ensures it cannot replicate, and the vaccine cannot make the recipient sick.

Covaxin uses a ‘dead’ or inactivated virus that is incapable of infecting anyone, but can instruct the immune system to make antibodies.

The source underlined, however, that the technical advisory group was yet to make a formal recommendation to the government as it was still examining the question of administering booster doses.

If and when the recommendation for a booster is made, beneficiaries vaccinated with Covishield, Sputnik V, and are likely to have multiple options.

— Hyderabad-based Biological E’s Corbevax: A vaccine built on the protein sub-unit platform, differing from inactivated whole-cell vaccines as it uses only the virus’ antigenic parts to trigger a protective immune response.

The Centre has ordered 30 crore Corbevax doses against an advance payment of Rs 1,500 crore, and the candidate is likely to get emergency-use authorisation in the next two weeks.

— Serum Institute of India’s Covovax: A recombinant nanoparticle protein-based vaccine, developed by US-based Novavax. Serum Institute of India has already received emergency-use authorisation in The Philippines.

— Bharat Biotech’s intranasal vaccine: Sources said this vaccine, administered through the nasal route, could be announced in the second half of January.

— India’s first mRNA Covid-19 vaccine, developed by Pune-based Gennova Biopharmaceuticals: The Centre has said Gennova was likely to produce 6 crore doses. Unlike mRNA vaccines developed by Pfizer-BioNTech and Moderna, this vaccine will not require ultra-cold storage and can be stored at 2-8°C.

Several expert bodies around the globe have recommended mRNA vaccines as booster doses. In September, the UK’s expert body advised that Pfizer’s mRNA vaccine be used as a booster, irrespective of the vaccine used in the primary schedule.