Why Indian scientists think boosters are essential to combat Omicron

Amid debates on the effectiveness of existing COVID vaccines against new variant Omicron, Indian scientists have said they can be a good defence against the disease. Antibodies tend do go down over six months or so after the second dose of COVID vaccine. Since a big chunk of the fully vaccinated population in India had its second dose more than six months ago, a booster shot would be essential, said the scientists.

A booster dose, as the name suggests, boosts the number of circulating antibodies, thus preventing the onset of symptomatic Omicron infection. This could be the most viable way to prevent the spread of the contagion, especially among the aged and the immunosuppressed.

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While the World Health Organization (WHO) is yet to take a stand on boosters, The Union Health Ministry has said the Centre is considering a booster administration drive, though no decision has been taken yet.

How boosters help

Once COVID vaccination is completed — that is, two shots are given — the effectiveness of the vaccine against infection declines by around 18.5 percentage points over the next six months. This is referred to as waning protection. This is of particular concern to the elderly and the immunocompromised, who lack the ability to fight the disease on their own.

A booster dose increases the antibody levels higher than that achieved by the initial vaccination course. For instance, researchers found, protection against the Delta variant from two doses was slightly lower than against the original strain; however, a booster dose brings it on par.

Last week, UK Health Security Agency (UKHSA) said a booster dose of Covishield vaccine offers up to 75% immunity from symptomatic Omicron infection. However, medical professionals from other parts of the world, including India, have said a booster shot of any vaccine raises antibody levels substantially.

Advancing the second shot

Dr Shahid Jameel, an eminent virologist, was quoted as saying by a PTI report that a booster shot pushes up the number of circulating antibodies and bolsters protection against symptomatic Omicron infection. Jameel had earlier headed the advisory group to the Indian SARS-COV-2 Genomics Consortia (INASACOG).

While the West is debating on boosters, a large majority of Indian have taken just the first shot of COVID vaccine. Jameel said those who got only the first dose of Covishield ought to be given the second one in 8-12 weeks, rather than the currently prescribed 12-16 weeks.

Indians can be given one of four booster doses, he said. These are: Covaxin for those who took Covishield earlier, and vice-versa, DNA vaccine ZyCov-D, and protein vaccines Covovax or Corbevax.

Dr T Jacob John, former director of the ICMR’s Centre of Advanced Research in Virology, has suggested vaccinating children immediately. For one, the Indian child population is fully unvaccinated, and can thus act as a reservoir. Also, he said, Omicron cases are alarmingly numerous among children in south African countries.