Why is the pre-school arm swelling sometimes so large?

Repeated doses of the diphtheria and tetanus components can produce a bigger local reaction, so this booster often causes more swelling than the infant doses did. It is uncomfortable rather than dangerous and settles within a few days, but any spreading redness with fever should be seen by a doctor.

Is this the same as the six in one vaccine?

No. The six in one (Hexavalent) adds Hib and hepatitis B and is given to babies. The four in one is the pre-school booster and leaves those two out, because the infant doses already covered them.

DTaP/IPV Vaccine: Schedule & Side Effects

Protects against: Diphtheria, Tetanus, Whooping cough, Polio
How given: Single injection in the upper arm.
Doses: A single pre-school booster, between three and six years depending on the country.
Reactions: Moderate

About this vaccine

DTaP/IPV combines four vaccines in one injection and is used as the pre-school booster in the UK, Australia and the Philippines. In the UK it is known as the four in one booster and given at three years four months; Australia gives it at four years. It tops up the protection built in infancy, before a child starts school and mixes with many more children.

What it protects against

Disease

Diphtheria

A bacterial infection that can block breathing and damage the heart.

Disease guide Disease

Tetanus

A serious infection caused by bacteria entering through wounds.

Disease guide Disease

Whooping cough

A highly contagious cough that is especially dangerous for young babies.

Disease guide Disease

Polio

A viral infection that can cause permanent paralysis in young children.

Disease guide

When it's given

United KingdomNHS · 2026

3 years 4 monthsBooster

View full schedule

AustraliaATAGI · 2026

4 yearsBooster

View full schedule

PhilippinesPIDSP · 2026

4-6 yearsBooster

View full schedule

Ages follow the schedules listed above. Your pediatrician may adjust timing for your child.

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How it's given

Single injection in the upper arm. This vaccine covers multiple infections in a single dose, reducing the number of separate injections needed at each visit.

Side effects & safety

A sore or swollen arm is common and can look more dramatic than it is, sometimes covering a good part of the upper arm before settling over a few days. A mild fever can follow.

How babies usually reactModerate

A mild fever or fussiness is fairly common for a day or two. This is a sign the immune system is responding normally.

When to call your doctor: if fever exceeds 40°C, lasts more than 2 days, or your child seems unusually unwell.

Alternatives & related vaccines

DTaPProtects against diphtheria, tetanus and whooping cough.Vaccine guide HexavalentA single shot protecting against six infections, including polio and hepatitis B.Vaccine guide PentavalentA single shot protecting against five infections, including hepatitis B and Hib.Vaccine guide

Common questions

Sources

The complete routine immunisation schedule · UK Health Security Agency, 2026.

Information on this page is compiled from authoritative public health sources and written in TinyDose's own voice. It is intended for general understanding only. Always follow your pediatrician's guidance.

Other vaccines

BCG OPV IPV DTwP All vaccines

From the blog

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This information is provided by TinyDose for general understanding only and is not medical advice. Vaccine names, ages and doses can vary by country, brand and individual circumstances. Always follow the guidance of your pediatrician or local health authority for your child’s vaccination schedule.

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