Why do smallpox and BCG vaccines leave scars?

Until 1979, all children were immunized against smallpox. This serious viral disease was eradicated in 1980 thanks to a worldwide vaccination campaign led by the World Health Organization (WHO). For many seniors, this vaccine left a scar on their upper left arm.

This mark, round and fairly wide, about two centimeters, deep and with irregular contours, is the result of the administration of the live vaccinia virus via a bifurcated needle, that is to say with two points. "When administering the vaccine using a bifurcated needle, a multiple puncture vaccination technique is used and a small drop of blood appears at the vaccination site," says the World Health Organization (WHO). Before it heals, the vaccinated area saw a papule appear on the skin.

BCG, only for certain populations

BCG, an acronym for Bacillus Calmette-Guérin, is the vaccine against tuberculosis. This infectious disease, usually pulmonary and highly contagious, is caused by the bacterium Mycobacterium tuberculosis. Until 2007, this vaccine was indicated for all children. Now, it is only for certain populations. These include children under 5 years of age who have an identified risk factor for tuberculosis, because they were born in or have resided in a country where tuberculosis remains a high prevalence.

This vaccine is administered by intradermal injection. This method can cause a small ulcer that, upon healing, leaves a scar less noticeable than that of the smallpox vaccine. Although less pronounced, this scar is also located on the left arm, usually at the shoulder.

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