Vaccines Explained: Normal Reactions, When to Postpone, and What Happens If You Miss One

Vaccination is one of modern medicine's most cost-effective interventions. But what actually worries parents usually isn't whether to vaccinate — it's "is this fever normal?", "can she have it with a cold?", and "do we start over if we missed one?" This piece answers those.

Normal reactions

Local: redness, swelling, a firm lump and tenderness at the injection site — usually settling in 1–3 days. A cool compress helps (no heat, no rubbing).

Systemic: low to moderate fever, irritability, sleepiness, poor appetite — typically within 24–48 hours, resolving on their own.

A different timeline: live attenuated vaccines like MMR can cause fever and rash 5–12 days later. That's a normal immune response, not a problem with the vaccine.

Management: rest, fluids, and weight-dosed antipyretics if genuinely uncomfortable. Bathing afterwards is fine — just don't rub the site, and keep it clean and dry.

Seek care immediately for

• Breathing difficulty, facial or throat swelling, or widespread hives within 30 minutes (anaphylaxis) — which is exactly why you wait 30 minutes at the clinic
• High fever persisting beyond 48 hours
• Lethargy, seizures, or inconsolable high-pitched crying for more than 3 hours
• Rapidly spreading redness or pus at the injection site

True contraindications are rarer than you think

Postpone for:

• Current fever (especially moderate to high) or acute infection
• An acute flare of serious chronic illness

Not contraindications (go ahead):

• A mild cold or runny nose without fever
• Mild eczema, or currently using topical steroid cream
• Breastfeeding
• Prematurity (vaccinate by actual birth date, not corrected age)
• Someone at home being pregnant
• A mild fever after a previous dose

Genuine absolute contraindications are few: severe allergy to a vaccine component, a previous severe reaction to the same vaccine, live vaccines in severe immunodeficiency. Your doctor makes these calls — you don't need to guess.

If you miss a dose

Good news: in almost all cases you don't restart the series. Immune memory doesn't reset because the gap got longer — just complete the remaining doses as advised.

Bring your immunisation record to the clinic and let the staff plan the catch-up. Intervals that are too short can reduce effectiveness, so follow the minimum spacing rather than compressing it yourself.

Two persistent myths

• "Vaccines cause autism": traced to a fraudulent, retracted paper whose author lost his licence. Studies covering millions of children since have found no association
• "Several shots at once overwhelm the immune system": infants handle enormous antigen loads daily; combined vaccines add a negligible amount. Co-administration is rigorously safety-tested and reduces both clinic trips and missed doses

One important note

Immunisation schedules differ by country and region — which vaccines are funded, which are optional, and how doses are spaced all vary. Follow your local immunisation record and the clinic staff's schedule; this article covers general principles only.

Compiled from mainstream immunisation consensus. Not medical advice — discuss specific decisions with your paediatrician or immunisation clinic.