A low-grade fever and a small, tender swelling at the injection site are expected after the 6-week vaccinations — they're a sign the immune system is responding, not a sign something went wrong. Most babies are back to themselves within a day or two, with simple comfort measures at home.

What's normal after the 6-week shots

The 6-week visit usually includes several vaccines together, which is exactly why mild reactions are so common at this check-up specifically.

  • A mild fever, generally under 38.5°C (101.3°F), appearing within the first 24 hours and settling within a day or two
  • Redness, warmth, and a small swelling at the injection site, in one or both thighs depending on how many vaccines were given
  • Fussiness or crying more than usual, especially when the leg is touched or moved
  • Reduced appetite or sleepiness for a day or so after the shots
  • A small, firm lump at the injection site that can take a few weeks to fully settle — this is different from acute swelling and is a separate, usually harmless finding on its own

A fever and a sore thigh in the first day or two after vaccination is your baby's immune system doing exactly what the vaccine is meant to make it do. It's the exceptions below — not the fever itself — that need a call.

What actually helps at home

  • Keep your baby comfortable with normal feeding on demand — babies often want to feed more for comfort in the hours after vaccination, which is fine.
  • A cool, damp cloth over the injection site can ease local swelling and tenderness.
  • Dress your baby lightly rather than bundling up, since overheating makes a mild fever feel more uncomfortable than it needs to.
  • Paracetamol, if your doctor has advised a dose for your baby's weight, can help with fever or fussiness — don't give any medication without checking the right dose for a baby this young first.
  • Gentle movement of the leg, like normal nappy changes and handling, doesn't harm the injection site and can help your baby stay comfortable rather than guarding the leg.

When to call your doctor

  • Fever of 38.5°C (101.3°F) or higher, or any fever that doesn't start settling within 48 hours
  • Swelling that is spreading, increasingly red, hot, or hardening rather than gradually softening — this can suggest a local infection rather than an ordinary reaction
  • Your baby is inconsolable for several hours, or crying in a way that sounds different from their usual cry
  • Your baby seems unusually floppy, very difficult to wake, or isn't feeding at all
  • A rash appears, especially one that doesn't fade when you press on it
  • Fever appears after the first 48 hours, since that's less likely to be a straightforward vaccine reaction and more worth checking for another cause

Why the thigh specifically

Vaccines given to young infants are injected into the thigh muscle because it's the largest, most reliably muscular site available at this age — the arm muscle isn't developed enough yet to be a reliable injection site in a 6-week-old. When two or three vaccines are given at the same visit, they're often split between the two thighs, which is why some babies react in one leg more than the other, or in both.

Frequently asked

Can I give paracetamol before the vaccination to prevent a reaction?

This isn't generally recommended as routine practice — giving paracetamol preventively, before any fever or discomfort appears, isn't shown to clearly help and is sometimes discouraged because of a theoretical effect on the vaccine's own immune response. Treating a fever or discomfort after it appears, with your doctor's advised dose, is the standard approach instead.

Is it normal for the swelling to feel like a hard lump, even after the redness goes away?

Yes. A small, firm nodule can persist at the injection site for several weeks after the initial redness and tenderness have resolved. This is usually harmless and gradually fades on its own, but mention it at the next check-up if it's still there or seems to be growing rather than shrinking.

How long does the fever usually last?

Most vaccine-related fevers peak within the first 24 hours and resolve within 48 hours. A fever that persists beyond two days, or that starts after that window, is less typical for a straightforward reaction and is worth a call to your doctor.

Can my baby have a bath after the vaccination?

Yes, a normal bath doesn't harm the injection site. Just be gentle over the area if it's visibly tender, and pat rather than rub it dry.

Should I delay the next round of vaccines if my baby reacted this time?

A mild, expected reaction like this is not usually a reason to delay future vaccines. If the reaction was more severe — a very high fever, significant swelling, or any allergic-type symptoms — discuss it with your doctor before the next scheduled dose so they can advise on how to proceed.