6. Antibiotics, Vaccines, and Disease Prevention

Antibiotics are drugs that kill or slow the growth of bacteria. They target structures unique to bacterial cells — most commonly the cell wall or bacterial ribosomes — without harming human cells.

How antibiotic resistance develops (review):
Random mutations give some bacteria resistance. Antibiotics kill susceptible bacteria but leave resistant ones to multiply. Overusing or misusing antibiotics speeds this process up. The GED® frequently asks you to explain this using natural selection logic.

Vaccines work by training the immune system without causing disease:

1. A vaccine introduces antigens — harmless pieces of the pathogen (proteins, weakened or inactivated virus, or mRNA instructions to make the antigen).
2. The immune system mounts a response and creates memory cells.
3. If the real pathogen arrives later, the memory cells recognize it immediately and destroy it before symptoms develop.

Types of vaccines:

• Live-attenuated (weakened) — MMR (measles, mumps, rubella), varicella (chickenpox).
• Inactivated (killed) — flu shot (injected form), polio (injected).
• Subunit/protein — Hepatitis B, HPV (just pieces of the pathogen).
• mRNA — COVID-19 vaccines (mRNA teaches cells to make the spike protein antigen).

Herd immunity: when enough of a population is immune (through vaccination or past infection), the pathogen cannot spread easily and even unvaccinated individuals are protected indirectly.

Other prevention strategies: handwashing, safe food handling, vector control (mosquito nets, insecticides), clean water supply, and quarantine/isolation.