Vaccination Side Effects Guide
This guide provides general information about common reactions after vaccinations. If you're concerned about any symptoms, always contact your pediatrician.
Why Do Side Effects Happen?
Vaccines work by training your baby's immune system to recognize and fight specific diseases. When your baby receives a vaccine, their body recognizes the vaccine components as "foreign" and mounts an immune response—this is exactly what we want to happen.
Mild side effects are actually a sign that the vaccine is working and your baby's immune system is building protection. Most reactions are mild and resolve within 1-3 days without any treatment.
Common Side Effects (Usually Normal)
According to the CDC and AAP, the following reactions are common after vaccination and typically resolve within 1-3 days.
Injection Site Reactions
- Pain/tenderness: Baby may cry when the area is touched
- Redness: The injection site may appear red or pink
- Swelling: Mild swelling around the injection site
- Lump: A small, firm bump may form at the injection site
Whole-Body Reactions
- Fever: Typically 100-101°F (37.8-38.3°C), sometimes higher
- Fussiness/irritability: More sensitive and crying than usual
- Decreased appetite: May eat less than normal
- Sleepiness: May sleep more than usual
- Mild rash: Some vaccines (like MMR) may cause a light rash 7-12 days later
Vaccine-Specific Reactions
DTaP (Diphtheria, Tetanus, Pertussis)
Injection site pain and swelling are more common with DTaP than other vaccines. Reactions may be more noticeable after the 4th and 5th doses. Up to 1 in 4 babies experience fussiness after DTaP.
MMR (Measles, Mumps, Rubella)
Mild fever or rash may appear 7-12 days after vaccination. This is caused by the weakened measles virus in the vaccine and is not contagious. About 1 in 6 children develop a fever after MMR.
Varicella (Chickenpox)
A mild chickenpox-like rash (a few spots) may develop 1-3 weeks after vaccination. This is rare (about 4% of children) and usually very mild.
Rotavirus (Oral Vaccine)
May cause mild diarrhea, vomiting, or fussiness. Contact your doctor immediately if you notice blood in stool or severe vomiting.
PCV13 (Pneumococcal)
About half of babies become drowsy after PCV13. Temporary loss of appetite and injection site tenderness are also common.
How to Comfort Your Baby
For Fever
- Dress your baby in light clothing
- Keep the room at a comfortable temperature
- Offer extra fluids (breast milk, formula, or water for older babies)
- If fever is 100.4°F (38°C) or higher, you may give acetaminophen (Tylenol)
- Ibuprofen (Advil, Motrin) can be used for babies 6 months and older
Important: Do NOT give fever reducers before vaccination as prevention. Give them only after symptoms appear. NEVER give aspirin to children.
For Injection Site Pain/Swelling
- Apply a cool, damp cloth to the area for 10-15 minutes
- Do NOT rub or massage the injection site
- Bathing is fine, but don't scrub the injection site
- Move or exercise the arm/leg to reduce soreness
For Fussiness
- Hold and cuddle your baby more than usual
- Offer comfort nursing or a pacifier
- Don't force feeding if appetite is low
- Keep the environment calm and quiet
- Skin-to-skin contact can be very soothing
When to Call the Doctor
While serious reactions are rare, contact your pediatrician or seek medical care if you notice any of the following:
Seek Emergency Care Immediately
- Difficulty breathing or wheezing
- Swelling of face, lips, or throat
- Pale or blue skin color
- Unresponsiveness or extreme lethargy
- Hives or rash spreading across the body
- Seizure (convulsions)
Note: Severe allergic reactions (anaphylaxis) usually occur within minutes to hours after vaccination. This is why doctors recommend waiting 15-30 minutes at the clinic after shots.
Call Your Doctor
- Fever over 104°F (40°C)
- Fever lasting more than 3 days
- Redness or swelling at injection site that keeps getting bigger
- Inconsolable crying for more than 3 hours
- Severe or persistent vomiting or diarrhea
- Refusing to eat or drink
- Any symptoms that concern you
After Vaccination: What to Do
- Stay at the clinic: Wait 15-30 minutes after vaccination to watch for immediate reactions
- Rest at home: Avoid strenuous activities on vaccination day
- Monitor temperature: Check for fever, especially in the first 24-48 hours
- Watch the injection site: Some redness and swelling is normal, but it shouldn't keep growing
Should I Delay the Next Vaccination?
If your baby had a reaction to a previous vaccine, tell your pediatrician before the next appointment.
- Mild reactions (low fever, fussiness): Usually okay to proceed with scheduled vaccinations
- Moderate reactions (high fever, prolonged crying): Discuss with your doctor; vaccination may still proceed with monitoring
- Severe reactions (seizure, severe allergic reaction): Doctor will evaluate whether to continue with that specific vaccine
- Currently sick: Mild cold is usually okay; postpone if there's high fever or serious illness
Reporting Side Effects
In the United States, you can report vaccine side effects to the Vaccine Adverse Event Reporting System (VAERS):
- Website: vaers.hhs.gov
- Anyone can file a report—parents, patients, or healthcare providers
- Reporting helps monitor vaccine safety
For serious reactions, you may be eligible for compensation through the National Vaccine Injury Compensation Program (VICP).
The Bottom Line
Mild side effects after vaccination are normal signs that your baby's immune system is working. Most symptoms resolve within 1-3 days without any intervention.
However, trust your parental instincts. If something doesn't seem right or you're worried about your baby, don't hesitate to call your pediatrician. It's always better to check and get reassurance.
Use our Vaccination Scheduler to keep track of your baby's immunization schedule and never miss an important shot.