A clear case for booster shots

Global studies show that vaccine immunity wanes after six months. Get boosters ready

Several global studies, both in laboratory settings and based on real-world data, have shown that vaccine effectiveness against Covid-19 starts decreasing after a certain time period, widely believed by experts to be around four to six months after the administration of the second dose of the vaccine. These studies have also shown that people above the age of 45, especially those who have comorbid conditions, are particularly prone to severe disease after the six-month mark.

On December 22, 2021, at a time when the world was at the cusp of the Omicron wave (which has since become waves), the World Health

Organization released a statement on booster doses for Covid-19 vaccination. The United Nations health agency analysed data from four of the world’s most heavily used vaccines — Pfizer-BioNTech’s Comirnaty, Moderna’s Spikevax, Astrazeneca’s Covishield, and Johnson & Johnson’s Ad26.COV2.S — and observed that there was a considerable decline in immunity with time. It said that in adults above 50, protection against severe Covid-19 decreased by about 10% at the six-month mark, and by 32% against symptomatic disease. In another study, which looked at the waning of immunity in Covishield, researchers at the University of Edinburgh started seeing a visible drop in immunity around three months after people were given their second shot. Compared with two weeks after receiving a second dose, there was a fourfold rise in the chance of death and hospitalisation four months from the second dose, which became a fivefold jump in five months.

To be sure, none of these studies is India-specific, but to look at the national context, nearly 185 million people, or 53% of all Indians above 45 years received their second shot of the vaccine four months ago, of which 150 million (43% over the age of 45) did so five months ago, and 36% at least six months ago. All of this is the government’s own data. Experts say the studies add to the argument that India must make available booster shots to this population cohort, and progressively to everyone over 18 years of age. Currently, only those over 60 are eligible for boosters in India. And while the Omicron wave may have bought India some time in terms of natural immunity among the masses, the sooner the issue of wider booster coverage is dealt with, the better. It’s still not too late — but may soon be.