Forget herd immunity targets for Covid-19 vaccines: Variants have queered the pitch, target universal vaccination

India is meeting only a small fraction of its target on sample-processing for genomic analysis.”>This has meant India is meeting only a small fraction of its target on sample-processing for genomic analysis.

Experts, including the Biden administration’s chief medical adviser Dr Anthony Fauci, are now warning that focusing on a herd immunity threshold (HIT) will be futile for the long-term control of Covid-19. For one, there’s vaccine hesitancy and, second, there is SARS CoV-2’s ability to mutate into variants that confer it increased immune-escape and transmissibility that needs to be reckoned with. Assuming even a vaccine cover as high as 70%—a proxy for the HIT held to be effective for the original variants—30% of the population would remain susceptible to circulating strains.

This, leaving aside considerations of ‘breakthrough’ strains and vaccine efficacy numbers. As such, the possibility of the virus evolving into variants that have greater immune escape and even higher transmissibility can’t be ignored. Add to this the chances of variants with similar characteristics originating in countries that have low levels of vaccination. Not enough vaccination cover could then mean getting trapped in a cycle of vaccine-innovation/redundancy, fuelled by emergence of newer and newer strains.

It is therefore vital India aims for universal Covid-19 vaccination and achieves the widest possible cover, while aiding efforts to ensure vaccine-access for poor countries. Both the UK variant, in circulation in some states including Delhi, and the double-mutant variant (B.1.617) detected in India and 15 other countries have high transmissibility; B.1.617 has greater immune-escape capabilities, too.

The government seems to have already dropped the ball controlling the spread of variants. Insacog—the laboratory consortium tasked with genomic analysis of variants in circulation in the country—has been processing samples well under its capacity. This has meant India is meeting only a small fraction of its target on sample-processing for genomic analysis.

And, as per a recent Reuters report, Insacog had flagged the double-mutant to the health ministry before March 10, warning that infections could quickly rise in parts of the country but the health ministry didn’t seem to share its concern in its statement on the double-mutant. Science must continue to inform policy and everyone must be vaccinated so as to minimise the chances of unvaccinated persons fostering viral evolution. Even with reduced case fatality and low rates of serious morbidity, a very transmissible virus with enhanced immune-escape capabilities can still overwhelm the healthcare facilities resulting in a high number of deaths.

To vaccinate large numbers—indeed, for universal vaccination cover—the Centre and the states must make the vaccine accessible, even free, for the economically weaker sections. There are multiple databases—from the SECC data to RTE EWS registrations and Jan-Dhan accounts—that can be used to identify beneficiaries; the Rs 35,000 crore allocation for vaccination in FY22 can be topped up if necessary. Crucial to this would be contracting large supplies of vaccines that have demonstrated good results in trials. The cost would be a small fraction of GDP, but the exercise could pay huge dividends.