Is it normal for a baby to have fever after vaccination?

Yes. Mild to moderate fever (up to 38.5C / 101.3F) is an expected reaction and shows the immune system is responding to the vaccine. It usually appears 6 to 24 hours after the shot and lasts 1 to 3 days. Use acetaminophen (paracetamol) as directed by your pediatrician if needed.

How long do vaccine reactions last?

Most local reactions (pain, redness, swelling) last 1 to 3 days. Fever usually resolves within 24 to 48 hours. Fussiness and drowsiness are common in the first 24 hours. If symptoms persist beyond 72 hours or worsen, consult your pediatrician.

Should I give fever medicine before vaccination to prevent reactions?

It is not recommended. Studies show that preventive use of antipyretics may reduce the immune response to the vaccine. Use fever medicine only if fever or discomfort appears after vaccination, as directed by your pediatrician.

Are severe allergic reactions to vaccines common?

Severe allergic reactions (anaphylaxis) are extremely rare, occurring in about 1 in every 1 million doses. This is why it is recommended to stay at the vaccination site for 15 to 30 minutes after the shot. Healthcare professionals are trained to identify and treat these reactions.

My baby has a lump at the injection site. Is this normal?

Yes, a small firm nodule (lump) at the injection site is a common local reaction, especially with intramuscular vaccines. It usually resolves on its own within 2 to 4 weeks. Do not squeeze or massage it. If it increases in size, becomes very red, or drains fluid, see your pediatrician.

Vaccine Reactions in Babies and Children: What Is Normal and When to Worry

Your baby just got vaccinated and now has a fever, is fussy, or has a red spot at the injection site? First of all: take a deep breath. The vast majority of vaccine reactions are mild, expected, and a sign that the immune system is working. In this guide, I explain what is normal, what to do at home, and when to see a pediatrician. For the complete schedule, see our 2026 baby vaccination guide.

Common Reactions: What to Expect After Vaccination

According to the Brazilian Society of Pediatrics (SBP) and the World Health Organization (WHO), the most frequent reactions are mild and self-limiting. They occur because your child's immune system is learning to defend itself — which is exactly the purpose of vaccination.

Local Reactions (at the injection site)

Pain and tenderness: Present in up to 80% of injectable vaccines. Improves within 24 to 48 hours.

Redness (erythema): A red area around the injection site. Normal and resolves in 2 to 3 days.

Swelling (edema): Mild local swelling. May last up to 3 days.

Lump (nodule): A small firm area at the injection site, especially after intramuscular vaccines. May take 2 to 4 weeks to disappear.

Systemic Reactions (whole body)

Fever: Temperature up to 38.5°C (101.3°F) is expected. Usually appears 6 to 24 hours after the shot. See how to manage fever in babies and check our normal temperature chart.

Fussiness and crying: Very common in the first 24 hours, especially in young babies.

Drowsiness: Your baby may sleep more than usual on vaccination day. This is normal and part of the immune response.

Decreased appetite: May refuse one or two feedings. Continue breastfeeding on demand.

Reactions by Vaccine Type

Each vaccine has a specific reaction profile. Knowing what to expect helps you prepare:

Vaccine	Most Common Reactions	Duration
Pentavalent/Hexavalent	Fever, local pain, fussiness	1 to 3 days
Meningococcal B	Fever (more intense), fussiness, local pain	1 to 2 days
Meningococcal C/ACWY	Mild local pain, low fever	1 to 2 days
Pneumococcal	Local pain, fever, drowsiness	1 to 2 days
MMR (Triple Viral)	Fever and rash (5 to 12 days after)	2 to 5 days
Influenza (Flu)	Local pain, low fever	1 to 2 days
Rotavirus (oral)	Fussiness, mild diarrhea	1 to 3 days

What to Do After Vaccination

For Pain and Local Swelling

• Apply a cold compress (not ice directly) for 10 to 15 minutes
• Move the vaccinated limb to help with absorption
• Do not massage the area firmly
• Dress your baby in comfortable clothing

For Fever

• Acetaminophen (paracetamol) as directed by your pediatrician (never aspirin in children)
• Maintain hydration with breast milk, formula, or water
• Use light clothing and keep the room well ventilated
• Monitor temperature regularly

For Fussiness

• Offer extra cuddles and comfort
• Breastfeed more frequently if your baby wants
• A warm bath can help calm your baby — see our sleep tips

When to See a Doctor

Warning Signs After Vaccination

• Fever above 39.5°C (103.1°F) or lasting more than 72 hours

• Inconsolable crying for more than 3 hours

• Intense redness spreading beyond 5 cm from the injection site

• Difficulty breathing, wheezing, or facial swelling

• Extreme drowsiness — baby difficult to wake

• Purple spots or bleeding

• Seizure (rhythmic involuntary movements)

If your baby shows any of these signs, seek medical attention immediately or see your pediatrician.

Myths About Vaccine Reactions

Myth: "If there was a strong reaction, my child can't get more vaccines"

Fact: Mild and moderate reactions are not a contraindication for future doses. Only severe allergic reactions (anaphylaxis) contraindicate that specific vaccine. Your pediatrician evaluates each case individually.

Myth: "Giving fever medicine before prevents reactions"

Fact: Studies published in The Lancet show that prophylactic use of acetaminophen before vaccination can reduce antibody production. Use it only if discomfort appears after the shot.

Myth: "Multiple vaccines on the same day overload the immune system"

Fact:A baby's immune system handles thousands of antigens daily. All vaccines on the schedule combined represent a tiny fraction of this capacity. Giving multiple vaccines on the same day is safe and recommended.

Myth: "If there was no reaction, the vaccine didn't work"

Fact: The absence of a reaction does not mean the vaccine failed. Many children develop full immunity without any symptoms. Protection does not depend on the presence of reactions.

Rare Adverse Events

In extremely rare cases, vaccines can cause more serious adverse events. Transparency is part of good medical information:

Anaphylaxis: Severe allergic reaction (1 in 1 million doses). Occurs within the first 15 to 30 minutes. This is why you should always remain at the vaccination site after the shot.

Febrile seizure: Associated with post-vaccine fever (not the vaccine itself). Occurs in predisposed children and is generally benign.

Hypotonic-hyporesponsive episode: Baby becomes pale, limp, and less responsive. Rare and self-limiting. Does not leave lasting effects.

For Expat Families: What to Know

Brazil's vaccination schedule includes some vaccines not routinely given in the US, UK, or Europe (such as BCG and Yellow Fever). Reactions to these may be unfamiliar. Dr. Paula explains each vaccine and its expected reactions during your first consultation.

If your child has delayed vaccines from moving to Brazil, catching up may mean receiving several vaccines in a short period. This is safe, and I prepare families for the expected reactions.

My Recommendation as a Pediatrician

After many years vaccinating babies and children, I can say with confidence: the benefits of vaccines infinitely outweigh the risks of reactions. I discuss with each family during routine checkups which reactions to expect for each vaccine and how to manage them at home. You will never be alone in this process.