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Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
The key difference
Vaccinations prevent disease by stimulating the immune system to produce memory cells before infection occurs. Antibiotics treat bacterial infections by killing bacteria or preventing their reproduction. Antibiotics do not work against viruses.
Vaccinations and antibiotics are both weapons against infectious disease, but they work in completely different ways and are used in different situations. Knowing when each is appropriate: and why antibiotics cannot treat viral infections: is a frequently tested IGCSE concept.
Feature
Vaccination
Antibiotics
What it does
Prevents disease by training the immune system
Treats existing bacterial infections
When used
Before infection: as a preventive measure
After infection: to treat the disease
How it works
Introduces a dead or weakened pathogen (or parts of it) to stimulate the immune system to produce antibodies and memory cells
Chemicals that kill bacteria or inhibit their growth (e.g. By disrupting cell wall synthesis or protein synthesis)
Effective against
Specific diseases (each vaccine targets one pathogen)
Bacterial infections only
Works against viruses?
Yes: vaccines exist for many viral diseases (e.g. Measles, influenza, polio)
No: antibiotics cannot kill viruses because viruses reproduce inside host cells and lack the structures antibiotics target
Duration of effect
Long-term: memory cells provide lasting immunity (sometimes lifelong)
Short-term: only effective while being taken; does not prevent future infections
Antibiotics target specific features of bacterial cells, such as:
The bacterial cell wall (e.g. Penicillin prevents cell wall synthesis, causing the bacterium to burst)
Bacterial ribosomes (some antibiotics block protein synthesis in bacteria)
Bacterial DNA replication machinery
Viruses do not have cell walls, their own ribosomes, or independent metabolic machinery. Instead, they inject their genetic material into a host cell and hijack the host's own machinery to replicate. Since the virus uses the host's structures, an antibiotic cannot target the virus without also destroying the host cell.
Herd Immunity
When a large proportion of a population is vaccinated against a disease, the pathogen cannot spread easily because most people are immune. This protects even those who cannot be vaccinated (e.g. Very young babies, people with weakened immune systems). This concept is called herd immunity, and it requires a high percentage of the population (often 90–95%) to be vaccinated to be effective.
Try a comparison question (3 marks)
A student has influenza (flu), which is caused by a virus. Their parent wants to get them antibiotics. Explain why antibiotics would not be effective. [3]
Show the answer and marking guidance
Influenza is caused by a virus, not bacteria
Antibiotics only kill bacteria / inhibit bacterial growth
Viruses reproduce inside host cells and do not have the structures (e.g. Cell walls, ribosomes) that antibiotics target, so antibiotics have no effect
Original Cambridge-style practice written for this site.
Common comparison mistakes
When answering a compare question, write matched pairs rather than two separate descriptions.
Saying antibiotics kill viruses: they only work against bacteria