Welcome to World Immunization Week

Deepti Pradhan
5 min readApr 23, 2021

With global numbers reaching a staggering 145+ million cases and 3+ million deaths from Covid-19, April 24 marks the start of United Nation’s tenth observance of World Immunization week. The theme this year is “vaccines bring us closer”

Image courtesy Nick Youngson CC BY-SA 3.0 Alpha Stock Images

Immunizing people against a number of diseases is a well-established protocol recognized and recommended by the WHO and other medical agencies. However, it remains a matter of contention for a number of people, even in the face of this devastating Covid-19 pandemic.

In 1796, Edward Jenner, a country doctor in Gloucestershire, carried out his now famous experiment that led to a breakthrough in immunization against smallpox. Jenner had used the pus from a milkmaid infected with cowpox, and applied it to an incision on a child’s arm, which subsequently made the boy immune to smallpox. However, according to several sources, variolation — a method to immunize an individual against the smallpox virus (Variola), that involves taking material from an infected individual and applying it to an uninfected individual — was well established in Asia and the Middle East, long before that.

About 100 years after Jenner, Louis Pasteur made a significant modification in vaccines when he developed one against rabies: whereas Jenner had triggered protection to smallpox using live virus from the pus of a person infected with another less virulent disease (cowpox), Pasteur reduced the virulence (severity of infection) of the rabies virus by letting it dry out before administering it to a young boy who had been mauled by a dog.

The next major innovations in vaccine development came in a burst about 70 years later, and a leading force in these efforts was Maurice Hilleman and his colleagues at E.R. Squibb and Sons (now Bristol-Myers Squibb), and later at Merck & Co. Over the course of his career, Hilleman developed 40 vaccines, 14 of which are currently on recommended vaccine schedules. These vaccines typically contained either live-attenuated viruses (resulting in reduced virulence of the virus) — such as the measles, mumps, rubella, flu and chickenpox vaccines; or viruses that had been inactivated by either heat, radiation or chemicals — such as the polio and hepatitis A vaccines. Irrespective of whether a vaccine was made of a live-attenuated virus, or an inactivated one, the…

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Deepti Pradhan

Employed at Yale University, Deepti is primarily a scientist & patient advocate. She runs Tilde Cafe, a forum to make science accessible (www.tildecafe.org)