**1. Introduction**

Immunization is a global health and development success story, saving millions of lives every year. Vaccines reduce risks of getting a disease by working with your body's natural defenses to build protection. When you get a vaccine, your immune system responds. Immunization is a key component of primary health care and an indisputable human right. It's also one of the best health investments money can buy. Vaccines are also critical to the prevention and control of infectious-disease outbreaks. They underpin global health security and will be a vital tool in the battle against antimicrobial resistance. The two terms vaccination and immunization has been used synonymously over the time but the two terms differ in their meaning [1].

"Vaccination" as per definition is defined as the process of administering the biochemical product referred to as vaccine in the human body whereas "Immunization" is defined as the process by which body develops immunity against the disease [2].

Vaccines train the immune system to develop antibodies and protect against the disease. As per World Health Organization (WHO) there are number of vaccines which had been developed against number of diseases namely Diphtheria, hepatitis B, measles, mumps, pertussis, polio and many more. On similar grounds, to tackle the menace of COVID-19, various vaccines have been developed [3].
