Immunisation reactions and what is normal

Knowing what to expect after vaccination reduces the anxiety substantially and makes it easier to recognise the small number of situations that need attention.

The common reactions

Which occur in a significant proportion and resolve within a day or two.

Redness, swelling and tenderness at the injection site.

Irritability and being generally unsettled.

Reduced feeding.

Extra sleepiness or, less commonly, disturbed sleep.

Mild fever, usually within the first day or two.

And a small hard lump at the site, which may persist for weeks and is harmless.

The delayed pattern

Which catches parents out because nobody warns them.

Live vaccines such as MMR produce reactions on a different timescale.

Fever and sometimes a measles-like rash typically appear around six to ten days afterwards.

A mumps-like swelling of the salivary glands can appear around two to three weeks afterwards.

These are expected responses rather than the illnesses themselves, and the vaccine viruses are not transmitted from a healthy vaccinated child in the way natural infection is.

Knowing the timing prevents a great deal of alarm and prevents the reaction being attributed to an unrelated cause.

The BCG vaccine

Where the local reaction is dramatic and expected.

Given in some countries, it produces a small raised spot within weeks that develops into a blister or small sore, which may ooze and takes weeks to months to heal, leaving a small scar.

This is the normal course.

The area should be kept clean and dry, covered loosely if discharging, and left alone otherwise.

Review is needed for a large abscess, spreading redness or a swollen gland in the armpit.

Managing the reaction

Practically.

Extra cuddling and feeding.

Breastfeeding during or immediately after the injection has evidence for reducing pain, as does sucrose in newborns.

A cool cloth on the injection site if it is sore.

Paracetamol or ibuprofen at the correct dose for distress or fever.

Guidance in some countries specifically recommends prophylactic paracetamol with certain meningococcal vaccines because of the high fever rate — this is a specific exception to the usual advice, and worth asking about.

Do not put creams or plasters over the injection site beyond a simple dressing.

And keep the child comfortable rather than aiming for a particular temperature.

When to seek help

Features that are not typical reactions.

A high fever that does not settle, or any fever in a baby under three months.

A baby who is unusually drowsy, floppy or difficult to rouse.

A seizure.

Persistent inconsolable crying for hours.

Spreading redness, heat and swelling well beyond the injection site, particularly after twenty-four hours, which may indicate infection.

A rash that does not fade under pressure.

And any sign that this is an illness rather than a reaction, since a child can coincidentally become unwell after vaccination and attributing everything to the vaccine risks missing something.

Allergic reactions

Very rare and time-critical.

Anaphylaxis after vaccination occurs within minutes, which is why clinics ask you to wait afterwards and why vaccination is given in settings equipped to treat it.

Signs: swelling of the face or throat, difficulty breathing, widespread hives, pallor and floppiness, or collapse.

This requires immediate emergency treatment.

A previous anaphylactic reaction to a vaccine or its components requires specialist advice before further doses, and specialist immunisation clinics exist for exactly this.

Egg allergy is not a contraindication to MMR, which is a common misconception.

Reporting

Worth knowing about.

Most countries have a system for reporting suspected adverse reactions to vaccines and medicines, open to both clinicians and members of the public.

These systems are how safety signals are detected, and reporting is useful even for reactions that turn out to be common.

Keeping the record

Practical and frequently neglected.

Keep the vaccination record safe, since it is needed for childcare, school, travel and any move between countries.

Photograph it.

Note the date of any significant reaction.

And if doses were missed or the schedule interrupted, catch-up is always possible and no doses need repeating from the beginning.

General information only, not medical advice. Seek urgent care for a seizure, a non-blanching rash, breathing difficulty or an unwell child after vaccination.