Wait-and-watch on Covid booster dose

India’s vaccination programme against the coronavirus is in full swing and nearly 89 crore persons have already received the vaccine. Of these, 24 crore have been given both shots and 65 crore one shot of the vaccine. These numbers suggest that India’s fight against the virus is progressing effectively, with an unprecedented coverage of the population in a short period of time. The next few months are going to be crucial as the goal to vaccinate all the adult population of nearly 1.08 billion must be met by the end of 2021. The younger population of below 18 years is also waiting to be vaccinated so that the anticipated harm to them during the presumptive third wave can be thwarted.

The Delta variant of the coronavirus had wreaked havoc during the second wave in India due to its very high infectivity. This highly virulent strain found the unvaccinated populace an easy target to inoculate and multiply. Now, after a few months, the situation seems to be under control and the daily cases are on the decline, although not as anticipated. However, the danger has not dissipated altogether and carelessness by people during the festive season may become precarious.

Reports from abroad show that many countries have suffered or are still hurting from the scourge of the Delta variant and a large number of cases is being reported daily even though these countries have already vaccinated significant portions of their populations. Though many of these cases involve unvaccinated individuals, some breakthrough infections have also been reported. This means that those who have received both doses of the vaccine are also getting infected, albeit with less severity and there are rare cases of mortality among the vaccinated lot.

Studies show that the antibodies acquired through vaccination or natural infection dwindle after a few months, which can pose the threat of breakthrough infections. Even though such cases may not get serious and fatal, these may cripple the hospital infrastructure if the infections spread in the population and would lead to another lockdown, affecting economic activities and livelihoods of many people. We cannot afford to endure it again.

To avert this scenario, many wealthy countries, including the US, France, Germany and Israel are administering booster shots to their older and vulnerable populations.

Do we in India also need to administer the booster shot to our population? Is it required? The answer could be both yes and no. It would depend upon the projection of the status of the pandemic in the near future. For example, if a new variant emerges similar to or more potent than the Delta variant,

it may pose a threat through breakthrough infections among even those who are vaccinated.

The daily cases of new infections have been declining recently, but the reporting of more than 20,000 cases per day on an average is still a worrisome indicator. New infections in unvaccinated individuals can become a breeding ground for the virus, which may churn up new variants, leading to another wave, as we saw in the first half of this year.

Further, the concern is also of breakthrough infections, which would indicate that either the protection offered by the vaccine has diminished over time or the virus has acquired a new form. If the daily cases of such breakthrough infections rise significantly, in such a scenario, a lockdown will be imminent and booster shots will be a way to manage the spread and severity.

Western countries are now facing the ravage of the Delta variant following India’s agonising experience with it in April-May this year. In the sero-survey conducted by the ICMR between June 14 and July 6, 2021, as much as 67.6 per cent of the general population aged six years or more had antibodies against the virus, while among the healthcare workers, this ratio was 85.2 per cent. These numbers suggest that a significantly high percentage of the population had been exposed during the second wave and developed immunity against the virus.

Genetic sequencing of the virus from the samples of patients reveals the presence of many Delta derivatives in patients, but they have not yet emerged as new entities. The Indian SARS-CoV-2 Genomics Consortium (INSACOG), which performs the sequencing of the virus genome, recently reported that AY.4, a sub-lineage of the Delta variant, is on the rise and was present in 44 per cent of the samples from Maharashtra in August 2021. Whether it is a matter of concern needs to be ascertained based on increased transmissibility, severity of infection and if it could cause breakthrough infections.

On the science of booster shots, experts have diverse opinions. One section is against the blanket use of booster shots. It argues that although antibody protection — which is a part of the humoral immunity — of the vaccine wanes with time as the titer of antibodies goes down. Nonetheless, protection through cellular immunity against severe disease and death would remain effective.

Others argue that booster shots would enhance the antibodies and prevent the infection rate from rising during a wave and may help decrease the patient’s viral load and infectivity and help avoid another lockdown.

Let us understand what a booster shot is. When a vaccine is administered, it induces the production of antibodies against the pathogen in the body of the individual receiving the shot. It is a part of the innate immunity which acts as the first line of defence and neutralises the pathogen as it enters the body. Simultaneously, the body also develops a repertoire of T cells — a part of the cellular and adaptive immunity — which kill the infected host cells and also neutralise the pathogens. In order to bolster this immunity against pathogens for a prolonged duration, more than one shot of the vaccine is required.

In the case of coronavirus, initially two doses of the vaccine were suggested to be sufficient. Many studies also suggest that the cellular immunity is still strong after several months of the second vaccine shot, but the antibody titer has declined. This has worried some experts in western countries and they want to bolster the antibody titer by giving another shot, the third one, as a booster dose amidst the ongoing wave caused by the Delta variant.

The priority in India must be to first vaccinate its whole population with at least one dose of the recommended two doses of the vaccine as soon as possible. Moreover, the vaccines are effective against the virus, including the variants reported so far. It is also ethically and morally incorrect to administer booster doses to a privileged few while the majority of the population is still partially vaccinated and waiting for the first or second dose.

Any plan to give the booster dose is not being mooted as yet, but when decided, it should be prioritised for the vulnerable and co-morbid people and the frontline workers.