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Parent’s Guide

Parent’s Guide: Vaccine Reactions

It is stressful to see your child uncomfortable after shots, but remember: reactions are usually a sign that the vaccine is working. Your child's body is building antibodies to protect them from serious disease.

1

🔎What is Normal? (Common Reactions)

Most reactions start within 12–24 hours and last 2–3 days.

Local Reaction:

Redness, swelling, and pain at the spot where the shot was given.

Note: With the DTaP vaccine, swelling can be large (over 3 inches) and last up to 7 days. This is common for the 4th or 5th dose.

Systemic Reaction:

Fever, fussiness, crying, sleeping more than usual, or poor appetite.

Delayed Reaction:

MMR & Chickenpox: These can cause a fever and a mild rash 1 to 4 weeks after the shot. This is normal and not contagious (unless fluid-filled blisters form).

2

🚨 When to Get Help

Call 911 Now

  • Severe allergic reaction: Trouble breathing, swallowing, or unable to wake up (starts within 10 mins to 2 hours).

Call Doctor Now or Go to ER

  • Age: Fever in a baby under 12 weeks old. (Do not give medicine before calling).
  • High Fever: Fever over 104° F (40° C).
  • Crying: Nonstop crying lasts more than 3 hours.
  • Rotavirus: Severe crying or vomiting follows the Rotavirus vaccine (could be rare bowel blockage called intussusception).
  • Immunity: Child has a weak immune system (cancer, HIV, sickle cell) and has a fever.

Contact in 24hrs

  • Redness at the shot site becomes larger than 2-3 inches.
  • Redness or pain gets worse after 3 days.
  • Fever lasts more than 3 days.
3

🏠Home Care Advice

You can usually treat these symptoms at home to make your child comfortable.

Treating the Shot Site

  • Massage: Gently massage the sore spot a few times a day.
  • Heat or Cold: Apply a heating pad (or warm washcloth) for 5-10 minutes to increase blood flow and reduce pain. You can use a cold pack if your child prefers it.
  • Hives: If the site is itchy, you can use 1% Hydrocortisone cream.

Treating Fever

  • Fluids: Offer unlimited cool fluids (formula/breastmilk for babies <6 months) to stay hydrated.
  • Clothing: Dress them lightly. Do not bundle them up.
  • Medicine:
    • Mild Fever (100°–102° F): Do not treat. This fever helps the immune system work.
    • High Fever (>102° F): If the child is uncomfortable, you can give Acetaminophen (Tylenol). Avoid giving pain meds BEFORE the shot, as it may reduce the immune response.
  • Warning: Never give Aspirin to children (risk of Reye Syndrome).
4

Specific Vaccine Notes

Some vaccines have unique side effects to watch for:

  • COVID-19: It is common to feel “flu-like” (chills, muscle aches, headache, fatigue) about 24 hours after the shot, especially the second dose.
  • Rotavirus: This oral vaccine can cause mild vomiting or diarrhea.
  • Chickenpox: A small rash (2–5 bumps) may appear 1-3 weeks later.
  • BCG (Tuberculosis): A blister forms 6–8 weeks later, drains, and leaves a scar. This is the expected result.

Medically Reviewed by Dr Michael Villadelgado
Disclaimer: This information is for educational purposes only. You assume full responsibility for how you use it. If you are unsure, always call your doctor.