How Vaccines Work: Immune Response Explained

What is this page about?

An explainer of how vaccines work, opening with Jenner's 1796 cowpox inoculation and the principle that exposing the immune system to a harmless version of a pathogen prepares it to defeat the real one. It walks the immune response step by step (antigen introduction and presentation, B-cell activation and antibody production, memory formation, and boosters), the types of vaccines (live-attenuated, inactivated, subunit, toxoid, mRNA, viral vector, and VLP), the mathematics of herd immunity, vaccine safety and development, efficacy versus effectiveness, and global access.

What has been corrected on this page?

Every accepted correction to this page is recorded with the exact change, so readers can see how the page improved over time.

1. 11 July 2026 · corrected by Emir Baycan

   WHO/CDC figure is ~25.5 million measles deaths prevented 2000-2019; Santoli 2020 does not support 37M

   Before

   vaccines prevented over 37 million deaths from measles alone (Santoli et al., 2020)

   After

   vaccines prevented an estimated 25.5 million deaths from measles alone (CDC/WHO, 2020)

   Why: Verified already correctly fixed in body content (25.5 million, CDC/WHO 2020). FAQ's only measles-related answer discusses herd immunity threshold percentages, an unrelated fact, not the deaths-prevented figure. Excerpt does not mention this figure. No further action needed.

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