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Immunization Reactions


  • Reactions to a recent immunization (vaccine)
  • Most are reactions at the shot site (such as pain, swelling, redness)
  • General reactions (such as a fever or being fussy) may also occur

Reactions to These Vaccines are Covered:

  • Chickenpox (varicella) virus
  • COVID-19 virus
  • DTaP (Diphtheria, Tetanus, Pertussis)
  • Hemophilus influenzae type b
  • Hepatitis A virus
  • Hepatitis B virus
  • Human Papilloma virus
  • Influenza virus
  • MMR (Measles, Mumps, Rubella)
  • Meningococcal
  • Polio virus
  • Pneumococcal
  • Rotavirus
  • Tuberculosis (BCG vaccine)

Symptoms of Vaccine Reactions

  • Local Reactions. Shot sites can have swelling, redness and pain. Most often, these symptoms start within 24 hours of the shot. They most often last 3 to 5 days. With the DTaP vaccine, they can last up to 7 days.
  • Fever with most vaccines begins within 24 hours and lasts 1 to 2 days.
  • Delayed Reactions. With the MMR and chickenpox shots, fever and rash can occur. These symptoms start later. They usually begin between 1 and 4 weeks.
  • Anaphylaxis. Severe allergic reactions are very rare. They start within 20 minutes. Sometimes can occur up to 2 hours after the shot. Vaccine health workers know how to treat these reactions.

Vaccine Free App

  • Vaccines on the Go app from Children's Hospital of Philadelphia
  • This free app can answer any vaccine questions you may have
  • It is fact-based and up-to-date

When To Call

Call 911 Now

  • Trouble breathing or swallowing
  • Not moving or very weak
  • Can't wake up
  • You think your child has a life-threatening emergency

Go to ER Now

  • Hard to wake up

Call Doctor or Seek Care Now

  • Fever in baby less than 12 weeks old. Caution: do NOT give your baby any fever medicine before being seen.
  • Fever higher than 104° F (40° C)
  • Fever after vaccine given and weak immune system (such as sickle cell disease, HIV, cancer, organ transplant, taking oral steroids)
  • Crying nonstop lasts more than 3 hours
  • Rotavirus vaccine followed by vomiting or severe crying
  • Your child looks or acts very sick
  • You think your child needs to be seen, and the problem is urgent

Contact Doctor Within 24 Hours

  • Redness around the shot becomes larger and more painful to touch after 3 days
  • Fever lasts more than 3 days
  • Fever returns after being gone more than 24 hours
  • Measles vaccine rash (starts day 6 to 12 after shot) lasts more than 4 days
  • You think your child needs to be seen, but the problem is not urgent

Contact Doctor During Office Hours

  • Redness or red streak around shot is larger than 2 inches (5 cm)
  • Redness, swelling or pain is getting worse after 3 days
  • Fussiness from vaccine lasts more than 3 days
  • You have other questions or concerns

Self Care at Home

  • Normal immunization reaction (mild redness and swelling, fever)

Care Advice

Treatment for Common Immunization Reactions

What You Should Know About Common Shot Reactions:

  • Immunizations (vaccines) protect your child against serious diseases.
  • Pain, redness and swelling are normal where the shot was given. Most symptoms start within the first 12 hours after the shot was given. Redness and fever starting on day 1 or 2 of the shot is always normal.
  • All of these reactions mean the vaccine is working.
  • Your child's body is making new antibodies to protect against the real disease.
  • Most of these symptoms will only last 2 or 3 days.
  • There is no need to see your doctor for normal reactions, such as redness or fever.
  • Here is some care advice that should help.

Vaccine Site Reaction: Treatment

  • Some pain, swelling and skin redness at the injection site is normal. It means the vaccine is working.
  • Massage: gently massage the injection site 3 or more times a day.
  • Heat: for pain or redness, apply a heating pad or a warm wet washcloth to the area for 10 minutes. Repeat as needed. Reason: will increase blood flow to the area. May apply cold if you prefer, but avoid ice.
  • No Pain Medicine: try not to give any pain medicines. Reason: pain medicines may reduce the body's normal immune response. Use local heat instead. Pain rarely becomes bad. If needed, use acetaminophen.
  • Hives at the Shot Site: if itchy, can put on 1% hydrocortisone cream (such as Cortaid). No prescription is needed. Use twice daily as needed.

Fever with Vaccines: Treatment

  • Fever with vaccines is normal, harmless and probably helpful. Reason: fever speeds up your body's immune system.
  • Fever with most vaccines begins within 12 hours and lasts 1 to 2 days.
  • For low grade fevers of 100-102° F (37.8 to 39° C), do not give fever medicines. Reason: they may reduce your body's normal immune response.
  • For fevers higher than 102° F (39° C), medicine may be given for discomfort. If needed, use acetaminophen.
  • Fluids. Encourage cool fluids in unlimited amounts. Reason: prevent dehydration. Fluids can also lower high fevers. For infants age younger than 6 months, only give formula or breastmilk.
  • Clothing. Dress in normal clothing. For shivering or the chills, use a blanket until it stops.

General Symptoms From Vaccines:

  • All vaccines can cause mild fussiness, crying and restless sleep. This is usually due to a sore shot site.
  • Some children sleep more than usual. A decreased appetite and activity level are also common.
  • These symptoms are normal. They do not need any treatment.
  • They will usually go away in 24-48 hours.

Call Your Doctor If:

  • Redness becomes larger than 2 inches (5 cm)
  • Redness becomes more painful after 3 days
  • Fever starts after 2 days (or lasts more than 3 days)
  • Redness or pain lasts more than 7 days
  • You think your child needs to be seen
  • Your child becomes worse

Specific Immunization Reactions

Chickenpox Vaccine:

  • Pain or swelling at the shot site for 1 to 2 days. (20% of children)
  • Mild fever lasting 1 to 3 days begins 14 to 28 days after the shot (10%). Give acetaminophen or ibuprofen for fever higher than 102° F (39°C).
  • Never give aspirin for fever, pain or within 6 weeks of getting the shot. Reason: risk of Reye syndrome, a rare but serious brain disease.
  • Chickenpox-like rash (usually 2 red bumps) at the shot site (3%)
  • Chickenpox-like rash (usually 5 red bumps) scattered over the body (4%)
  • This mild rash begins 5 to 26 days after the shot. Most often, it lasts a few days.
  • Children with these rashes can go to child care or school. Reason: for practical purposes, vaccine rashes are not spread to others.
  • Exception: do not go to school if red bumps drain fluid and are widespread. Reason: can be actual chickenpox.
  • Caution: if vaccine rash contains fluid, cover it with clothing. You can also use a bandage.

COVID-19 Vaccine

  • Injection site reactions. Pain and tenderness starts within 8 hours (90% of patients). Other local reactions are some swelling (10%) or skin redness (5%). Local symptoms usually last 1 to 3 days.
  • General body symptoms after the second dose. Fever (15%), chills (40%), tiredness (70%), muscle aches (50%) and headaches (60%). Runny nose and sore throat are more common with Omicron variant. Some other mild side effects are decreased appetite, nausea, dizziness, and increased sleep.
  • General symptoms start at about 24 hours. They usually last 1 day, sometimes 2.
  • Vaccines with 2 doses. Symptoms are more frequent after the 2nd vaccine.
  • Vaccines with one dose. Side effects were the same type, but a little less often.
  • Booster shots. Side effects much the same.
  • The vaccine does not cause any respiratory symptoms such as cough, runny nose, sore throat or shortness of breath.
  • It is impossible to get COVID-19 from the vaccine. Reason: there is no live COVID-19 virus in the vaccine.
  • Severe allergic reactions to the vaccine are very rare.

Diphtheria, Tetanus, Pertussis (DTaP) Vaccine:

  • The following harmless reactions to DTaP can occur:
  • Pain, tenderness, swelling and redness at the shot site are the main side effects. This happens in 25% of children. It usually starts within the first 12 hours. Redness and fever starting on day 1 of the shot is always normal. It lasts for 3 to 7 days.
  • Fever (in 25% of children) and lasts for 24 to 48 hours
  • Mild drowsiness (30%), fretfulness (30%) or poor appetite (10%) and lasts for 24 to 48 hours.
  • Large swelling over 4 inches (10 cm) can follow the later doses of DTaP. The area of redness is smaller. This usually occurs with the 4th or 5th dose. It occurs in 5% of children. Most children can still move the leg or arm normally.
  • The large thigh or upper arm swelling goes away without treatment by day 3 (60%) to day 7 (90%).
  • This is not an allergy. Future DTaP vaccines are safe to give.

Hemophilus Influenza Type B Vaccine (Hib):

  • No serious reactions reported.
  • Sore injection site or mild fever only occurs in 2% of children.

Hepatitis A Vaccine:

  • No serious reactions reported.
  • Sore injection occurs in 20% of children.
  • Loss of appetite occurs in 10% of children.
  • Headache occurs in 5% of children.
  • Most often, no fever is present.
  • If these symptoms occur, they most often last 1-2 days.

Hepatitis B Virus Vaccine (HBV):

  • No serious reactions reported.
  • Sore shot site occurs in 30% of children and mild fever in 3% of children.
  • Fever from the vaccine is rare. Any baby under 2 months with a fever after this shot should be examined.

Influenza Virus Vaccine:

  • Pain, tenderness or swelling at the injection site occurs within 6 to 8 hours. This happens in 10% of children.
  • Mild fever less than 103° F (39.5° C) occurs in 20% of children. Fevers mainly occur in young children.
  • Nasal Influenza Vaccine: congested or runny nose, mild fever.

Measles Vaccine (part of MMR):

  • The measles shot can cause a fever (10% of children) and rash (5% of children). This occurs about 6 to 12 days after the shot.
  • Mild fever less than 103° F (39.5°C) in 10% and lasts 2 or 3 days.
  • The mild pink rash is mainly on the trunk and lasts 2 or 3 days.
  • No treatment is needed. The rash cannot be spread to others. Your child can go to child care or to school with the rash.
  • Call Your Doctor If:
    • Rash changes to blood-colored spots
    • Rash lasts more than 3 days

Meningococcal Vaccine:

  • No serious reactions.
  • Sore shot site for 1 to 2 days occurs in 50%. Limited use of the arm occurs in 15% of children.
  • Mild fever occurs in 5%, headache in 40% and joint pain in 20%
  • The vaccine never causes meningitis.

Mumps or Rubella Vaccine (part of MMR):

  • There are no serious reactions.
  • Sometimes, a sore shot site can occur.

Papillomavirus Vaccine:

  • No serious reactions.
  • Sore injection site for few days in 90%.
  • Mild redness and swelling at the shot site (in 50%).
  • Fever higher than 100.4° F (38.0° C) in 10% and fever higher than 102° F (39° C) in 2%.
  • Headache in 30%.

Pneumococcal Vaccine:

  • No serious reactions.
  • Pain, tenderness, swelling or redness at the injection site in 20%.
  • Mild fever less than 102° F (39° C) in 15% for 1-2 days.

Polio Vaccine:

  • Polio vaccine given by shot sometimes causes some muscle soreness.
  • Polio vaccine given by mouth is no longer used in the U.S.

Rotavirus Vaccine:

  • Most often, no serious reactions to this vaccine given by mouth.
  • Mild diarrhea or vomiting for 1 to 2 days in 3%.
  • No fever.
  • Rare serious reaction: intussusception. Risk is 1 in 100,000 (CDC). Presents with vomiting or severe crying.

BCG Vaccine for Tuberculosis (TB):

  • Vaccine used to prevent TB in high-risk groups or countries. It is not used in the US or most of Canada. Note: this is different than the skin test placed on the forearm to detect TB.
  • BCG vaccine is given into the skin of the right shoulder area.
  • Timing: mainly given to infants and young children.
  • Normal reaction: after 6 to 8 weeks, a blister forms. It gradually enlarges and eventually drains a whitish yellow liquid. The blister then heals over leaving a scar. The raised scar is proof of BCG protection against TB.
  • Abnormal reaction: abscess (infected lump) occurs in the shoulder or under the arm. Occurs in 1% of patients.
  • Call Your Doctor If:
    • Blister turns into a large red lump
    • Lymph node in the armpit becomes large


Barton Schmitt MD, FAAP
Disclaimer: this health information is for educational purposes only. You, the reader, assume full responsibility for how you choose to use it.
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