Vaccination and Antibiotics
Vaccination
Vaccination involves injecting a dead or weakened (attenuated) form of the pathogen, or parts of it (e.g. surface antigens), into the body. This stimulates an immune response without causing the disease.
How Vaccines Work
1. A vaccine containing a dead/inactive pathogen (or its antigens) is injected into the body
2. White blood cells (lymphocytes) detect the antigens on the pathogen
3. Lymphocytes produce antibodies specific to those antigens
4. Memory cells are created and remain in the body
5. If the real, live pathogen enters the body later, memory cells recognise the antigens immediately
6. Antibodies are produced rapidly and in large quantities — the pathogen is destroyed before it can cause illness
7. The person is immune
Herd Immunity
If a large proportion of the population is vaccinated, the disease cannot spread easily because there are too few susceptible people for the pathogen to infect. This protects:
- Babies who are too young to be vaccinated
- Immunocompromised individuals (e.g. people with weakened immune systems)
- People who cannot be vaccinated for medical reasons
The threshold for herd immunity varies by disease (e.g. measles requires approximately 95% vaccination coverage).
Advantages and Disadvantages of Vaccination
| Advantages | Disadvantages |
|---|---|
| Prevents serious illness and saves lives | Some people may have side effects (usually mild — soreness, fever) |
| Can eradicate diseases (e.g. smallpox was eradicated in 1980) | Rarely, severe allergic reactions can occur |
| Herd immunity protects vulnerable people | Does not always give 100% protection |
| Reduces NHS costs from treating diseases | Some people refuse vaccines (ethical/personal reasons), reducing herd immunity |
| Reduces time off work/school | Vaccines must be stored correctly and may require multiple doses |
Antibiotics
Antibiotics are drugs that kill or prevent the growth of bacteria inside the body. They do not work against viruses.
Examples:
- Penicillin — discovered by Alexander Fleming in 1928; kills bacteria by preventing cell wall formation
- Amoxicillin — treats chest infections, UTIs
- Erythromycin — alternative for penicillin-allergic patients
Why Antibiotics Do Not Work on Viruses
Viruses reproduce inside host cells, using the host cell's machinery. Antibiotics target bacterial structures (e.g. cell walls, ribosomes) that viruses do not have. Antiviral drugs exist but are harder to develop because damaging the virus may also damage the host cell.
Antibiotic Resistance
Antibiotic resistance occurs when bacteria evolve to survive exposure to antibiotics. This is a major global health concern.
How resistance develops:
1. Within a population of bacteria, there is natural genetic variation (random mutations)
2. Some bacteria may have a mutation that makes them resistant to an antibiotic
3. When the antibiotic is used, it kills the non-resistant bacteria, but the resistant ones survive
4. The resistant bacteria reproduce, passing the resistance gene to offspring
5. Over time, the whole population becomes resistant — this is natural selection
6. The antibiotic is no longer effective
MRSA (methicillin-resistant Staphylococcus aureus) is a well-known antibiotic-resistant strain.
Reducing Antibiotic Resistance
- Only prescribe antibiotics when necessary — never for viral infections
- Patients must complete the full course of antibiotics (even if feeling better) to ensure all bacteria are killed
- Restrict the use of antibiotics in agriculture (livestock farming)
- Develop new antibiotics to stay ahead of resistance (this is slow and expensive)
- Good hygiene in hospitals to prevent the spread of resistant bacteria
Other Treatments
Painkillers (e.g. paracetamol, ibuprofen):
- Treat the symptoms of disease (pain, fever) but do not kill pathogens
- Do not cure the disease — the immune system must still fight the infection
Antiviral drugs:
- Specifically target viruses (e.g. antiretrovirals for HIV)
- Harder to develop than antibiotics because viruses live inside cells
Drug Development and Testing
New drugs must be tested for safety, efficacy (does it work?), and dosage:
1. Preclinical testing — tested in labs on cells and tissues, then on animals to check for toxicity and efficacy
2. Phase 1 clinical trial — tested on a small number of healthy volunteers to check for side effects and safe dosage
3. Phase 2 clinical trial — tested on a small number of patients with the disease to check efficacy
4. Phase 3 clinical trial — large-scale trial on thousands of patients, often using a double-blind method with a placebo (a dummy treatment)
A placebo is used so that any improvement can be attributed to the drug and not the placebo effect (psychological improvement from believing you are being treated).
In a double-blind trial, neither the patient nor the doctor knows who is receiving the drug or placebo — this prevents bias.
Exam Tips
- Vaccines contain dead or inactive pathogens — never say "live" unless specifying attenuated (weakened)
- Antibiotics kill bacteria only — stating they do not work on viruses is almost always worth a mark
- When explaining antibiotic resistance, use the term natural selection and mention random mutation as the source of variation