Childhood Vaccines: Reliable Information, Common Reactions, and When to Seek Care

An independent educational resource prepared by Mark M. Simonian, MD, FAAP

Sources checked: August 12, 2026     |     Medical review completed: August 12, 2026

This page is for general education only and does not replace individualized medical advice. This resource does not establish a doctor-patient relationship. For questions about your own child, contact your child's current healthcare professional.

Magnolia Pediatrics, Valley Children's Healthcare

2497 E. Herndon Avenue, Suite 101, Clovis, CA 93611     |     559-538-3070

Vaccines help protect children from serious infections. Because recommendations, products, and schedules can change, this page does not reproduce a vaccine schedule. Use the current CDC schedule, the Vaccine Information Statements for vaccines offered at the visit, and your child's healthcare professional for an individualized plan.

Urgent Warning Signs - Check This First

Serious allergic reactions after vaccination are rare, but they need emergency care. A child who looks severely ill after any shot needs medical assessment.

CALL 911 NOW

  • Trouble breathing or swallowing; swelling of the lips, tongue, mouth, or throat; widespread hives with breathing or throat symptoms; blue or gray lips or face; fainting with ongoing concerning symptoms; or a child who is limp or unresponsive.

  • A seizure, a child who cannot be awakened, or another life-threatening emergency.

GET EMERGENCY MEDICAL CARE NOW

  • A baby younger than 3 months (12 weeks) with a rectal temperature of 100.4 F (38 C) or higher, even if the baby was recently vaccinated. Do not give fever medicine before the baby is evaluated unless a healthcare professional has specifically directed it.

  • A child who looks very ill, has repeated vomiting with severe belly pain after rotavirus vaccine, has severe headache or stiff neck, or has a concerning symptom that is rapidly worsening.

CONTACT YOUR CHILD'S HEALTHCARE PROFESSIONAL TODAY

  • Fever that is high, persists longer than expected, returns after improving, or occurs with a child who seems much sicker than expected.

  • Redness, swelling, or pain at the shot site that is getting larger or more painful after several days; drainage or pus; or a red streak from the site.

  • Crying that is difficult to console, a new widespread rash, new weakness, ongoing dizziness, or any reaction that concerns you.

  • A previous severe allergic reaction, a condition affecting the immune system, or a question about whether a vaccine should be given, delayed, or caught up.

What Is Common After a Vaccine?

  • Temporary soreness, redness, or swelling where a shot was given.

  • Mild fever, fussiness, tiredness, reduced appetite, headache, or body aches, depending on the vaccine and the child's age.

  • Some vaccines can have later reactions. For example, fever or a mild rash can occur days to weeks after certain live vaccines. The Vaccine Information Statement explains expected timing for each vaccine.

  • Most mild reactions improve within a few days. Comfort measures, rest, fluids, and the care plan recommended by the child's healthcare professional are usually sufficient.

Before and During a Vaccine Visit

  • Bring the child's immunization record and questions. Ask which vaccines are planned and request the Vaccine Information Statement (VIS) for each one.

  • Tell the healthcare professional about a prior reaction to a vaccine, known allergies to vaccine components, an immune condition, current medicines, or a moderate or severe illness. A mild illness is often not a reason to delay vaccination, but the clinician should decide.

  • Use calm, honest reassurance. Holding, feeding, distraction, and a soothing voice can help infants and children through vaccination. Adolescents should sit or lie down and remain observed afterward if they are prone to fainting.

Reliable Vaccine Information

  • Use the current CDC consumer schedule rather than an old printed schedule or an internet graphic. The child's schedule may differ because of age, prior vaccines, travel, health conditions, or a need for catch-up doses.

  • A Vaccine Information Statement is a CDC document that explains benefits and risks for a specific vaccine. Vaccine providers are required to provide the appropriate VIS before covered vaccines are given.

  • Ask the child's healthcare professional to review questions one at a time. It is reasonable to want clear information about expected benefits, common reactions, rare serious reactions, and the plan for your child.

Keeping Records and Catching Up

  • Keep a copy or photograph of the immunization record and bring it to health visits, school or child-care registration, and travel-planning visits.

  • If a dose is delayed or records are incomplete, contact the child's healthcare professional. CDC catch-up guidance uses prior doses and intervals; families should not restart a series without professional advice.

  • Ask early about vaccines needed for travel, school requirements, new health conditions, or medications that affect immunity.

Related Guides

Sources and Medical Review

Sources checked August 12, 2026. Medical review completed August 12, 2026.