DNA Explainer: Should booster doses of COVID-19 vaccines be given?

Amid the spread of the new Omicron variant of the COVID-19, many countries have started administering booster doses of the vaccine. India is still to take any decision regarding this. The Health Ministry on Friday said that India is still examining the possibility of administering booster shots.

Vaccination is a very important tool in fighting viruses. A vaccine imitates an infection. It activates the body's immune system to produce antibodies and memory T-cells without causing illness. Antibodies are the body's first response to fight getting infected, while T-cells protect against severe disease.

Health experts are of the opinion that boosters will be required for continuing protection from the COVID-19 virus. They also stress that second-dose coverage is of high priority. While some of the experts are of the opinion that increasing coverage and offering targeted boosters to vulnerable sections should go simultaneously.

What is a booster dose?

The booster dose is an additional shot given after the protection provided by the original shots has begun to decrease over time.

The logic behind giving booster doses of a vaccine is to help people maintain their level of immunity for a longer period of time.

The immunity period developed by an infection or by vaccination will last depending upon various factors.

This is because antibodies decay over time and even memory T-cells or antigen-specific T cells will die after a few years or months.

Prior to COVID-19, in the past boosters were recommended for smallpox prevention every three to five years.

Tetanus toxoid boosters are also recommended today for adults and pregnant women after childhood vaccination.

What study says on vaccines

ICMR-Regional Medical Research Centre, Bhubaneswar study showed a significant drop in antibodies within four months of vaccination.

A study on the immune response to mRNA vaccines found declining antibody levels at six months, but durable memory B cell and T cell responses.

The findings published in the Science journal earlier this year showed most of the B cells were able to cross-bind with the Alpha, Beta and Delta variants.

A study in the US showed that antibodies reduce by more than 80% six months after receiving the second dose of the Pfizer-BioNTech mRNA vaccine.

Some experts in India say the goal should be vaccination of the entire eligible population with the recommended doses rather than boosters.

What studies claim on booster doses

BioNTech and Pfizer claim a three-shot course was able to neutralise the Omicron variant in a laboratory test.

The US vaccine manufacturers say that the third dose of the COVID-19 vaccine increased neutralizing antibodies by a factor of 25.

A recent study by the Indian Council of Medical Research scientists suggested the use of Covishield booster shots to fight emerging variants.

The study which is yet to be peer-reviewed evaluated the neutralizing potential of blood samples from people who received two doses of Covishield.

Data from Israel and UK indicate booster dose of one of the widely used mRNA-based vaccines sharply lowers risk of catching SARS-CoV-2.

Several months after Israel became the first country in the world to make boosters available to all, its daily case counts remain low.

If community transmission is high, boosters would help in controlling viral spread, says Dr Sanjay Pujari, member, ICMR national task force on COVID.

IMA President Dr J A Jayalal stressed the need to roll out a booster for healthcare and frontline workers and immunocompromised persons.