Vaccines & Preventive Medicines Used-For Guides

What Vaccines & Preventive Medicines covers

This section covers medicines given to prevent illness rather than treat it: vaccines, and preventive treatments such as prophylactic antibiotics and antiretrovirals used to stop an infection taking hold.

Prevention is a different proposition from treatment, and the difference shapes how these medicines are used. You take them while well. There is no symptom to tell you they are working, and no obvious feedback when a dose is missed. What they deliver is the absence of something — an infection that never happened.

The section covers three kinds of thing. Vaccines train the immune system to recognise an organism in advance. Preventive antimicrobials such as co-trimoxazole, dispensed here as Novatrim, are given continuously to people at particular risk of specific infections. Preventive antiretrovirals such as lamivudine and tenofovir are used to stop HIV establishing after exposure, or on an ongoing basis for people at substantial risk.

Several medicines in this section also appear as treatments elsewhere on the site. The ingredient is the same; the reason for taking it is not.

Browse individual used-for guides

Most searched questions in this topic

How the guides in this section differ

Vaccine or medicine. A vaccine prompts your own immune system to build protection, generally over weeks, and that protection can last years. A preventive medicine works only while you are taking it, and protection stops when it does.

Continuous or single-course prevention. Some prevention is ongoing for as long as the risk lasts. Some is a defined course after a specific exposure, where starting promptly is what makes it work.

Same ingredient, different purpose. Co-trimoxazole treats infections and also prevents them in people at particular risk. Lamivudine and tenofovir treat HIV and are also used preventively. Dose, duration and monitoring differ between those roles.

Timing is part of the medicine. Vaccine schedules have intervals for a reason, and post-exposure prevention has a window measured in hours. In this section, when you take something is as important as what.

Kind of prevention	How it protects	How long protection lasts	If a dose is missed
Vaccine	Trains your immune system to recognise the organism	Often years; some need boosters	Usually resume the schedule rather than restart — ask the clinic
Ongoing preventive antimicrobial	Suppresses the organism while taken	Only while taking it	Take when remembered; tell the clinic if misses are frequent
Ongoing preventive antiretroviral	Blocks the virus establishing	Only while taking it	Missed doses reduce protection and risk resistance
Post-exposure prophylaxis	Stops an infection taking hold after exposure	The course only	Start within hours; generally not begun beyond 72 hours

The bottom row is the one to remember, because it is the only entry on this page where a delay of a day removes the option entirely.

Safety, accuracy and next-step checks

These guides explain what a preventive medicine is used for. They do not assess your risk, recommend a vaccine or set a schedule — those depend on age, health, occupation, travel and exposure, and belong with a clinician.

Points that matter here:

After a possible HIV exposure, act immediately. Post-exposure prophylaxis should start as soon as possible, ideally within hours and generally within 72 hours. Go to a clinic or emergency department; do not research first.
Preventive medicines only work while taken. Missed doses reduce protection, and with antiretrovirals also risk resistance.
Keep to the vaccine schedule. Where a vaccine needs more than one dose, the interval is part of how it produces protection. If a dose is late, ask rather than assuming you must restart.
Check what you need before travelling, well in advance. Some vaccines need weeks to take effect, and some need multiple doses.
Tell the clinician if you are pregnant or immunocompromised. Some vaccines are unsuitable, and alternatives or timing adjustments exist.
Expect mild reactions. A sore arm, mild fever or tiredness for a day or two is a common and unremarkable response. Severe or persistent reactions should be reported.
Keep a record. Vaccination records are needed for school, some jobs and some travel, and are far easier to keep than to reconstruct.

South African public clinics provide childhood vaccinations and HIV prevention services free of charge.

Frequently asked questions

How is a vaccine different from a preventive medicine? A vaccine trains your immune system to build its own protection, which persists after the course. A preventive medicine protects only while you keep taking it.

Why is the same medicine listed for both treatment and prevention? Because several genuinely are used for both, at different doses and durations. The ingredient does not change; the purpose does.

I missed a vaccine dose in a course. Do I start again? Usually not — most schedules can be resumed rather than restarted. Ask the clinic, which can check against the specific schedule.

How quickly must post-exposure prevention start? As soon as possible. Effectiveness falls with delay and it is generally not started beyond 72 hours. Treat it as urgent.

Are vaccine side effects a sign something is wrong? A sore arm, mild fever or fatigue for a day or two is a normal immune response. Anything severe, or lasting longer, should be reported to a health professional.