What is the science behind COVID-19 vaccine booster shot

Even as the world is busy providing the first and second doses of the COVID-19 vaccines to its citizens, countries like the United States and some other European countries have started giving a third dose of the vaccine called the booster shot to fight against the deadly coronavirus.

New data suggests that while the current plasmid DNA and mRNA vaccines have so far proven effective against COVID-19, the protection they offer may fade after a while. COVID-19 is a completely new virus that continues to evolve and mutate throwing the biggest challenge for experts.

The decision is also taken due to the fact that the Delta variant of the COVID-19 which is more infectious and spreads easily is driving a new surge of cases, including a rising number of breakthrough cases for fully vaccinated people. This is also responsible for why the attention has turned to the need for another COVID-19 vaccine dose.

Why do I need a third dose?
New research suggests that the protection the main two mRNA vaccines - Pfizer and Moderna give against COVID-19 might fade after several months.

The study was conducted on vaccinated people in Israel who mostly got the Pfizer shot. Israel began vaccination in December 2020 ahead of most countries.

The study indicates that as the Delta variant spread there was a correlation between receiving the vaccine at an earlier date and contracting a breakthrough case.

The study pointed out that patients vaccinated in January 2021 were 2.26 times more likely to contract a breakthrough infection than those vaccinated in April 2021.

It shows that more people are being exposed to the Delta variant and more vaccinated people are getting breakthrough infections than the initial data suggested.

The study conducted in Israel shows that the protection starts to fade around six months for some people from the time they become fully vaccinated.

How booster dose works?
There is an initial surge in the number of immune cells churning out antibodies and other molecules after vaccination, which then slowly drops.

This leaves behind a small pool of long-lasting 'memory' B and T cells that patrol the body for future infections by that pathogen.

A booster dose causes antibody-making B cells to multiply, elevating the levels of antibodies against the pathogen once again like after vaccination.

In time, the number of antibodies will decrease but the pool of memory B cells left behind will be larger than before, leading to a faster, stronger response.

Boosters also promote a process called affinity maturation, in which 'engaged' B cells, triggered by the vaccine travel to the lymph nodes.

Here, they gain mutations making the antibodies they produce bind to pathogens more strongly, potentially enhancing their potency.