Vaccination

Vaccination is a preventive procedure in which a weakened, killed, or partial form of a virus or bacterium — or a substance that mimics it — is introduced into the body to train the immune system to recognise and fight that specific infection in the future.

After the vaccine is given, your immune system treats the material as a threat and builds a defence, including special proteins called antibodies and memory cells. If you later encounter the real infection, your body can respond quickly and powerfully, often preventing illness or making it much milder. The vaccine itself does not cause the full disease.

Vaccination is used to protect individuals and communities from a wide range of infectious diseases. Your doctor or travel medicine specialist will recommend vaccines based on your age, health history, occupation, and travel plans.

• Childhood immunisation schedules: diseases such as measles, mumps, rubella, diphtheria, whooping cough (pertussis), tetanus, polio, and hepatitis B
• Respiratory infections: influenza (seasonal flu), COVID-19, and pneumococcal disease (a bacterial lung and blood infection)
• Travel-related infections: typhoid, hepatitis A, yellow fever, Japanese encephalitis (a viral brain infection), meningococcal disease, and rabies pre-exposure
• Infections common in specific groups: HPV (human papillomavirus, which can cause cervical cancer) for adolescents, shingles (a painful nerve rash caused by reactivated chickenpox virus) for older adults, and pneumococcal disease for the elderly
• Occupational exposure: healthcare workers, laboratory staff, and others with a higher-than-average risk of contact with certain infections

Some vaccines are not suitable for everyone. A doctor will usually advise against or delay vaccination in the following situations:

• Severe allergy (anaphylaxis) to a component of the specific vaccine
• Severely weakened immune system, for example due to certain cancers or immune-suppressing medicines — live vaccines in particular may need to be avoided
• Current moderate or severe acute illness — vaccination is usually postponed until recovery
• Pregnancy, for some types of live vaccines — the doctor will weigh the individual risk and benefit
• Previous severe reaction to the same vaccine

Most vaccines are well tolerated, and serious reactions are uncommon; many people experience only mild, short-lived effects at the injection site or feel briefly unwell as the immune system responds.

• Pain, redness, or swelling at the injection site — the most common reaction, usually settling within one to two days
• Low-grade fever, tiredness, headache, or muscle aches in the day or two after the vaccine
• Swollen lymph nodes (small glands in the body that filter infection) near the injection site
• Mild rash, particularly with some live vaccines such as MMR (measles, mumps, rubella)
• Fainting (vasovagal syncope) shortly after the injection — more common in adolescents; staying seated for a short time after vaccination reduces this
• Allergic reaction, ranging from hives (an itchy skin rash) to, rarely, anaphylaxis (a sudden, severe whole-body allergic reaction) — this is why clinics ask patients to wait and be observed after the injection
• With some specific vaccines, rare effects particular to that vaccine — your doctor will explain these when recommending a specific product

Vaccination generally requires very little preparation compared with surgical procedures. However, a few steps help the process go smoothly and safely.

Before your appointment, let the administering doctor or nurse know about any allergies you have, any medicines you are currently taking (including blood thinners or medicines that suppress the immune system), any recent illnesses, and whether you are pregnant or breastfeeding. There is no need to fast; you may eat and drink normally beforehand. Some doctors suggest staying well hydrated and avoiding alcohol for a day before and after, particularly for vaccines that can cause a mild fever response.

Pre-vaccination tests are not usually required for routine vaccines. For certain travel or specialist vaccines, or for people with complex medical histories, a doctor may first check blood tests to see if you already have immunity, or to assess whether your immune system is strong enough to handle a live vaccine.

The vaccination procedure itself typically involves the following steps:

• A brief health screening: the nurse or doctor asks about your current health, allergies, and vaccine history
• Identity and vaccine verification: your details are checked and the correct vaccine and dose are confirmed
• Site preparation: the skin — usually the upper arm, thigh, or sometimes the upper arm's deeper muscle — is cleaned with an antiseptic (a germ-killing solution)
• Administration: the vaccine is given as an injection into the muscle (intramuscular), just under the skin (subcutaneous), or, for some vaccines, as a nasal spray or by mouth — your doctor will use the route specified for that particular vaccine
• Immediate observation: you are asked to remain at the clinic for a period after the injection so staff can respond quickly if a rare allergic reaction occurs
• Documentation: the vaccine name, lot number, and date are recorded in your immunisation record

Recovery after vaccination is usually quick and straightforward. Most people leave the clinic feeling well and can return to their normal activities the same day, though mild soreness or fatigue may last a day or two.

• Stay at the clinic for the observation period your provider recommends — this is to monitor for any early allergic reaction
• A cool, damp cloth on the injection site can ease soreness and reduce swelling; avoid rubbing the area vigorously
• If a mild fever develops, staying well hydrated and resting usually helps; your doctor can advise on appropriate medicines to manage discomfort if needed
• Avoid strenuous exercise on the day of vaccination if your arm feels tender; light activity is generally fine
• Monitor for any unusual or worsening symptoms — difficulty breathing, rapid swelling of the face or throat, or a rash spreading beyond the injection site — and seek immediate medical attention if these occur
• Keep your immunisation record updated; for vaccines that require more than one dose, follow the schedule your doctor provides so that full protection is achieved
• For travel vaccines, note that some take several weeks to build full immunity, so planning vaccination well in advance of travel is important
• At your next routine check-up, let your doctor know which vaccines you have received so your overall immunisation history stays complete