Booster Dose

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Context

Health Ministry said India is still examining the possibility of administering booster shots of the Covid-19 vaccine, while noting that the World Health Organization (WHO) has not taken a stand on this.

What is a ‘booster’ dose?

Most Covid vaccines are administered in two doses, with a few given as a single dose.
A booster is an additional shot given after the protection provided by the original shot(s) has begun to decrease over time, so that people can maintain their level of immunity for longer.
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.

How long immunity developed by an infection or a vaccination lasts?

It depends upon various factors. For example, antibodies decay over time, and even memory T-cells will die after a few years or months.

The cells in our body deploy powerful countermeasures against viral infection. Antibodies, made by types of blood cells called B cells, are molecules that recognise and attach to parts of the virus. Other cells called T cells seek out and destroy virus-infected cells, removing the source of infection.

https://indianexpress.com/article/explained/explained-to-roll-out-booster-vaccines-or-not-to-7666860/