Childhood Vaccines: What Happens When, and What to Expect

The schedule, birth to 3

Most shots happen at routine well visits — at 1, 2, 4, 6, 9, 12, 15, 18, 24 and 30 months. The usual pattern: - Birth: hepatitis B, first dose — ideally within 24 hours. - 2 months: DTaP (diphtheria, tetanus, whooping cough), polio (IPV), Hib, pneumococcal (PCV), rotavirus, and the second hepatitis B dose. - 4 months: DTaP, polio, Hib, pneumococcal and rotavirus, second doses. - 6 months: DTaP, polio, Hib, pneumococcal, rotavirus (a third dose only for the 3-dose vaccine) and hepatitis B third doses — plus the first flu vaccine, every year from 6 months on, and the COVID-19 vaccine, which the AAP recommends from 6 months. (The first flu season takes two doses, at least 4 weeks apart.) - 12–15 months: MMR (measles, mumps, rubella), chickenpox (varicella), and the Hib and pneumococcal boosters. - 12–23 months: hepatitis A, two doses at least 6 months apart. - 15–18 months: DTaP, fourth dose. - RSV protection: either the RSV vaccine in pregnancy (32–36 weeks) or an antibody dose for the baby (nirsevimab or clesrovimab) in the first months, before or during RSV season — one or the other, depending on what happened in pregnancy.

Why so many, so young

The diseases these vaccines prevent are most dangerous in the first months of life, just as the protection passed on in pregnancy fades. Each dose builds the protection further, and the schedule spaces them so your baby is covered as early as possible. Combination vaccines mean fewer separate shots.

What to expect after shots

• A sore, red or slightly swollen spot where the shot went in is normal — a sign the body is responding to the vaccine. It usually starts within the first 12 hours.
• A mild fever is normal too, usually starting within a day and gone in 1 to 2 days. So are fussiness, crying, restless sleep, sleeping more than usual and a smaller appetite — most of it passes in 24 to 48 hours.
• The MMR and chickenpox vaccines work on a delay: a mild fever or rash can show up 1 to 4 weeks after the visit, not the next day — most often about a week after.
• Cuddles, fluids and rest fix most of it. You can gently massage the sore spot and put a warm, damp cloth on it for 10 minutes. For a low fever, the AAP suggests holding off on fever medicine — fever is part of the immune response the vaccine is trying to trigger. If the fever goes over 102°F (39°C) and your child is uncomfortable, acetaminophen can help. Never give aspirin.

When to check in

• Call the pediatrician if redness grows larger than 2 inches (5 cm), a fever starts more than 2 days after the shot or lasts more than 3 days, or redness or pain lasts more than 7 days.
• Call the same day for inconsolable crying, unusual drowsiness, or severe crying with vomiting in the week after a rotavirus dose; that combination can, rarely, mean a bowel blockage.
• Any fever in a baby under 3 months, 100.4°F (38°C) rectally or higher, is a call to the pediatrician right away, vaccine or not.
• Call 911 for hives, swelling of the face, or trouble breathing in the minutes after a shot. Severe allergic reactions are very rare, and when they happen they almost always start while you are still at the clinic.

If you fall behind

Life happens — an illness, a missed visit, a move. Catch-up schedules exist for exactly this, and a series almost never has to be restarted from the beginning. Tell your pediatrician and they will map out the catch-up doses. Keep the record (paper card or your state's registry) and bring it to every visit.

A note on the 2026 schedules

In 2026 the CDC and the AAP published different versions of the schedule. The AAP's 2026 schedule keeps routine immunization against 18 diseases and is the one most pediatric practices use. The CDC's version, released in early January 2026, dropped routine recommendations for several shots babies get — hepatitis A and B, rotavirus, flu and COVID-19 — moving them to high-risk groups or a conversation with your doctor. The schedule above follows the AAP's version. Your pediatrician decides what fits your child and when.