Older vaccines often used live but weakened viruses or bacteria that caused localised infection, triggering an immune response.

In the past, getting a vaccine often left a scar on your arm. Many people assumed that the scar meant the vaccine was working. Today, modern vaccines today don’t cause scarring. Does it mean they aren’t as effective? Not at all!

Older vaccines, like those for smallpox, measles, and BCG (tuberculosis), often used live but weakened viruses or bacteria. These could cause a small, localised infection, and trigger an immune response. This response sometimes led to redness, swelling, and even pus-filled lesions or scars. Additionally, older vaccines contained adjuvants (substances added to enhance the immune response) and preservatives that could cause severe local reactions. 

Modern vaccines are much different. Some are created by inactivating a pathogen, typically using heat or chemicals. Examples include the inactivated polio vaccine and the seasonal flu shot. While they may occasionally cause some redness or swelling, there are fewer instances of scarring.

Vaccine effectiveness is measured by the immune response, usually through antibody levels in the blood. The lack of visible reactions doesn’t mean that the vaccine isn’t working. Modern vaccines are tested to ensure that they are both effective and safe. According to the World Health Organization, vaccination currently prevents up to five million deaths every year from diseases like diphtheria, tetanus, pertussis, influenza and measles.

Read More : Vaccination averted 154 million deaths in 50 years: Study

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