Explained: The difference between booster shot and additional Covid-19 vaccine

In India, the National Technical Advisory Group on Immunisation (NTAGI) has recently met to discuss about the immediate need of administering extra doses of Covid-19 vaccine to the immunocompromised population, booster doses for those still unaffected and most importantly, child immunisation. In fact, an expert panel called Covid-19 task force has been established that is expected to come up with a comprehensive policy regarding all of the above.  

However, the common people have been in a state of dilemma ever since this news was published, as they are quite evidently unclear about the difference between booster shots and additional vaccines. We are here to clarify. 

What is an additional Covid-19 vaccine? 
An additional Covid-19 vaccine is nothing but a third dose, that is suitable for people who have successfully got themselves vaccinated twice and have moderate to seriously affected immune systems. This additional dose is expected to improve their response to the original vaccine. With the coronavirus mutating rapidly almost thrice every year, majority of the population might not develop immunity after double doses of vaccination. This additional dose is prescribed for such people to strengthen their immune system against the Covid-19 virus. 

The term ‘third dose’ was replaced by ‘additional dose’ because people who have taken a single dose from Johnson and Johnson as opposed to the double doses from mRNA vaccines will also be granted their extra doses. 

What is a booster shot? 
A booster shot is administered to enhance the magnitude of one’s immune system against a specific pathogen. The goal is to push the same original vaccine to strengthen protection by forming more and more antibodies.  

Hence the booster dose too is an additional dose. The difference that it is administered only when the immunisation effects of the original shots have naturally started to reduce over time. It is designed to help people lengthen their level of immunity. The aim of the booster shot is to signal the immune cells to re-interact when and if the virus attacks. 

What is the difference between the two? 
A booster shot is usually offered when a person has successfully finished the originally intended vaccine series and the protection against the virus has begun to fade away with the lapse of time.  

In contrast, an additional dose is given when people, already been affected by the virus and developed weakened immune system or to the ones who live with terminal ailments like cancer. This extra dose enables them to better their immune response and level up to that of unaffected, healthy population.