The relentless march of Covid’s second wave in India continues.

The daily case count has gone beyond 3.5 lakh cases per day, and deaths too have unfortunately crossed 3400, the second highest in the world after the United States.

Everybody including the health administration seems to be struggling with how to tackle and contain this monstrous surge. And the nervousness of the administration reflects in their somewhat knee-jerk reaction to give the go-ahead to all foreign-produced COVID-19 vaccines that have been granted emergency use authorization (EUA) in other countries.

The National Expert Group on Vaccine Administration for COVID-19 (NEGVAC) had already given EUA to a Russian viral vector vaccine Sputnik-V from the Gamaleya Institute. Another, vector vaccine, Johnson & Johnson’s (JNJ’s) Adenovirus 26 (Adv26) is possibly on track to getting a regulatory nod.

Two Covid vaccines, Covishield and Covaxin are already being presently used in the vaccination programme. And this programme has just opened up to everyone over 18 years.

Russian Direct Investment Fund (RDIF) has manufacturing contracts with multiple Indian companies and Sputnik-V is expected to be available soon. So, soon our vaccine basket would be studded with at least four different Covid vaccines.

But will they all be effective against the ongoing surge?

And will the large-scale vaccination control the ongoing surge?

The pace of vaccine inoculation in India is still far less than desirable. As of May 2nd, only 9.2% of the total population has received at least one dose and a meagre 2.0 % are fully vaccinated. It may take few years to reach anywhere near the threshold to achieve herd immunity (around 60%-70% based on the estimate with old variant D614G).

With the advent of a new, more transmissible variant, the estimate for a herd immunity threshold may further go up. Nevertheless, there is going to be a limited impact of large-scale vaccination on the ongoing transmission. Vaccines may have some utility for individual protection, but they may have little impact on the course of the ongoing pandemic. We are currently on the ascending limb of an outbreak propelled by a highly transmissible virus with a high reproduction number (Ro). The current variant is not only extremely transmissible but also has the ability of immune evasion.

Will the achievement of ‘herd immunity’ halt the ongoing surge?

To attempt achieving herd immunity with the current vaccines (whose effectiveness against the circulating variant is questionable) may turn out to be a futile exercise. We have the example of the Brazilian city of Manaus where a more virulent variant (P.1) ripped through the high ‘seropositivity cover’ of past infections to cause a huge outbreak. Further, there is confusion over what it means to reach herd immunity. The ‘herd immunity’ threshold is the point at enough people are immune (by vaccination or previous infection) to prevent a new epidemic from starting. It is NOT the point at which an ongoing epidemic disappears. When you reach ‘herd immunity, a pandemic is far from over.

The problem is that while a new epidemic can no longer start from scratch once you reach herd immunity when we reach this point for Covid we will still have the old epidemic underway. All the people who are currently infected will continue to transmit the disease after you reach the herd immunity threshold. They just will infect fewer than one additional person, on average. So, the achievement of the herd immunity threshold may not prevent the ongoing outbreak but may significantly diminish the chances of a future surge.

So, how does the administration halt the ongoing surge?

One important thing to keep in mind is that the herd immunity threshold depends on the transmissibility of the disease. Strict implementation of non-pharmaceutical interventions (mandatory universal masking, social distancing, gathering restrictions) around the herd immunity threshold is a very efficient way to reduce the total size of the epidemic, by reducing the overshoot. For this, we need strict lockdowns. Milder interventions like night curfew, weekend lockdown, etc may not work. An extended period is needed to break the viral chain. Implementing aggressive controls for even a short period around the herd immunity threshold reduces the overshoot and prevents many cases that would have occurred without controls.

Every large country has controlled fierce outbreaks of new variants by multiple lockdowns like UK, South Africa, France, etc. Only Israel could contain their epidemic with massive inoculations, but India is no Israel. There the variant was different (B117) which did not have any impact on vaccine effectiveness, the country population was small, and the employed vaccine was a highly potent one (Pfizer’s mRNA). Vaccines will have their impact, provided we choose and use them judiciously.

Judicious use of Covid vaccines: Need of the hour!

We are in a race against time to get global transmission rates low enough to prevent the emergence and spread of new variants. Put simply, the game has changed, and a successful global rollout of current vaccines by itself is no longer a guarantee of victory. Still, large scale vaccination may count provided we use them judiciously. We need to be judicious while planning our vaccination drive. It should have a significant impact at the population level and should counter any future surge. As stated above, we need to massively ramp up the speed of inoculation. The currently employed vaccines, Covishield and Covaxin may have limited impact on the major Indian variants, particularly newly detected variants having E484K mutation. The B1618 variant has this mutation which is known to have an ‘immune escape’ property, which means currently employed vaccines may be less efficacious. The presence of E484K mutation in the B1618 variant is particularly worrisome since this `immune evading’ mutant is also present in South Africa’s SA B1351. The AstraZeneca vaccine (parent vaccine of Covishield) vaccine failed to offer any protection against the South African variant, B1351. Even the Sputnik-V was found significantly less effective against the SA B1351 variant.

According to a recent study, Covaxin though seems to work against B117 and B1617, it has not been tested against any variant having E484K including B1618. Similarly, a study by the Centre for Cellular and Molecular Biology (CCMB) finds that Covishield also protects against B1617. Even the Sputnik-V was found significantly less effective against the SA B1351 variant.

Two covid vaccines, JNJ’s Adv26 and Novavax’s protein subunit vaccine have found to offer reasonable protection against the B1351 variant in the field efficacy trial in South Africa. Hence, both these vaccines have a better chance of providing good protection against the E484K mutation containing variant (B1618) than the other vaccines. This variant can spread widely and may soon replace the existing wild strain, D614G. Mass use of the vaccines effective against these new variants can build useful population immunity to prevent the next wave of the pandemic.

Ideally, the public health policies should be guided by science, not by the programmatic feasibility. Every effort should be made to take an evidence-based decision that may serve immediate and future purposes. There is no point inoculating billion people with a jab that may not accord requisite protection against the circulating virus.

(The writer is former National Convener, Indian Academy of Paediatrics, Committee on Immunization. Views are personal.)