Fighting Covid-19 with booster vaccination

SINCE the beginning of vaccination against Covid-19 a year ago, over 160 crore doses of two vaccines, Covishield and Covaxin, have been given till date. This is a remarkable achievement for India. Earlier this month, the government allowed an additional dose (precaution dose) to select categories of people. The recent spurt in cases due to the Omicron variant has prompted a large number of people who were earlier hesitant to go for the vaccine.

The development of Omicron as a new variant of concern in November and its higher transmissibility had brought back memories of the devastation caused by the Delta variant across the world. It has also brought to surface the spectre of some new and lethal variants developing in the coming months. Currently, while there is a steady increase in the overall number of cases in the country, a few metropolitan cities are showing signs of the ebbing of the wave. Projections suggest that the peak of the third wave will be in mid-February.

Recent data show that there are significantly lower deaths and hospitalisations in the ongoing third wave as compared to the second wave. A year ago, with over 3,80,000 new cases on April 30, there were over 3,000 deaths, but recently, with close to 3,20,000 new cases, the number of fatalities was 380.

This is attributed in part to the successful vaccination programme. While only two per cent of the people had been vaccinated at that time, now over 72 per cent of the eligible population is vaccinated. Figures from Mumbai showed that three-fourth of the deaths during this wave were in the unvaccinated people. The same has been the experience of some other countries.

Vaccines have been proven to prevent severe disease and, hence, reduce hospitalisation and death. Both of the widely used vaccines in India, Covishield and Covaxin, have fulfilled these expectations. However, several vaccination follow-up studies have shown that the levels of protective antibodies decline substantially after six-nine months of the second dose, more so in the elderly and immune-compromised.

A recent study from Hyderabad has reiterated that almost one-third individuals had antibody levels below the protective immunity levels after six months of the second dose. These individuals were mostly above 40 years with co-morbidities like hypertension and diabetes. However, despite achieving more than 70 per cent vaccination of the over 18-year-olds, we do not have much data from India on the waning of immunity over a period of time.

The other information lacking is data on the mix-and-match of different vaccines. In a small study, again from Hyderabad, antibody response was four-fold higher in those who received two different vaccines compared to those who got both doses of the same vaccine.

Western data suggest that a booster shot of a different platform vaccine than the first two gives a better protection. The results of the COV-Boost study from the UK showed that a third dose of Covishield resulted in over three-fold increase in neutralising antibodies, but the use of Novavax and Pfizer-BioNTech resulted in much higher augmentation. Data on the efficacy of boosters against Omicron are limited though. A recent report in The Lancet showed that a booster dose does increase the level of neutralising antibodies against the Omicron variant. While after two doses, protection against Omicron was not sustained, after the third dose (booster), the antibody response was more than 2.5 times stronger.

The Centre of Disease Control, USA, recently released three sets of its data. Booster doses were 90 per cent effective at keeping people out of hospital after they had become infected with the Omicron variant. The doses were also 82 per cent effective at preventing emergency department and urgent care visits. Previous researches in Europe and South Africa also showed that available vaccines are less effective against Omicron than the earlier versions of the coronavirus, but also that additional doses boost the virus-fighting antibodies to increase the chance of avoiding symptomatic infection.

Indian data on Covaxin has also shown an increase in neutralising antibodies by seven times after a third dose as compared to the placebo. Bharat Biotech has claimed that these antibodies effectively neutralise the Omicron variant as well.

Scientists have raised the issue of lack of more Indian data. With a centralised vaccine portal (CoWIN), we should have data on reinfection/breakthrough infection, level of antibodies generated and their decay on follow-up, effect of natural infection on immunity following vaccination and impact of mix-and-match of different vaccines as boosters.

There is also a need to study differences between India and other countries. We have a larger proportion of younger population and we encountered the Delta wave much before widespread vaccination was delivered. We could be having a more pronounced and sustained antibody response after natural infection with the Delta variant which was widespread in the second wave.

While booster shots have been definitely shown to protect against severe disease due to Omicron, India still has many people who have defaulted from the second dose. About 6.5 crore people have not yet received their scheduled second dose. States lagging in complete vaccination are Jharkhand, UP, Punjab, Manipur, Andhra Pradesh and Bihar. It is a matter of concern that three of these are going to the polls soon.

The government has rightly launched ‘ghar ghar dastak’, a doorstep vaccination programme, but more could be done. In the USA, incentives like free food coupons and free transport were offered to those missing the second dose. Another way could be to charge for a delayed vaccination. Some European countries have brought in ‘vaccine mandates’, to disallow unvaccinated individuals from public places, theatres and clubs etc. Healthcare workers are mandated in many countries to have complete vaccination. Unvaccinated individuals not only run the risk of disease themselves and transmit it to others, but also act as potential hosts for the virus to multiply and mutate further.

India has also initiated vaccination in the 15-17 year age-group. It is time to extend it to the younger children, especially when another vaccine, ZyCoV-D, has got approval for 12+ children. Extending vaccination to children is extremely important to confidently restart schools and colleges. We also have the option of using Corbevax (developed in collaboration with the Baylor College of Medicine, Texas) and Covovax (Indian name for Novovax) in our vaccination drive.

We must continue with the vaccination drive with vigour and extend the scope of vaccines and boosters to more groups of people. That will go a long way in our fight against Covid-19 in its current avatar or any of its future ones.