At the 4-month wellness visit, your baby receives five vaccines: DTaP (diphtheria, tetanus, and whooping cough), Hib (a type of bacterial meningitis), polio, pneumococcal disease, and rotavirus. All five are second doses, building on the first round given at 2 months. Depending on your pediatrician’s office, your baby may get as few as two needle pokes plus oral drops, or as many as four pokes plus drops.
The Five Vaccines at 4 Months
Each vaccine at this visit is the second dose in a multi-dose series. Here’s what they protect against:
- DTaP (dose 2 of 5): Protects against diphtheria, tetanus, and pertussis (whooping cough). Whooping cough is especially dangerous for young infants who can struggle to breathe during coughing fits.
- Hib (dose 2 of 3 or 4): Protects against Haemophilus influenzae type b, a bacterium that can cause meningitis, pneumonia, and serious throat infections in babies.
- IPV (dose 2 of 4): Protects against polio, which can cause paralysis.
- PCV (dose 2 of 4): Protects against pneumococcal bacteria, a leading cause of ear infections, pneumonia, and meningitis in young children. Your baby will receive either PCV15 or PCV20, both currently recommended.
- Rotavirus (dose 2 of 2 or 3): Protects against a virus that causes severe vomiting and diarrhea. This is the only one given as oral drops rather than a shot.
How Many Needle Pokes to Expect
Five vaccines doesn’t necessarily mean five needles. Many pediatricians use combination vaccines that bundle several vaccines into a single injection. Vaxelis, for example, combines DTaP, polio, Hib, and hepatitis B into one shot. Pediarix combines DTaP, polio, and hepatitis B. If your doctor uses Vaxelis, your baby could receive just two injections (Vaxelis plus the pneumococcal vaccine) and the rotavirus oral drops. With Pediarix, it’s typically three injections (Pediarix, Hib, and pneumococcal) plus the oral drops.
The shots are given in the thighs, which have plenty of muscle for intramuscular injection at this age. The rotavirus drops are squirted gently into your baby’s mouth and usually go down easily.
Why the Second Dose Matters
Babies are born with antibodies passed from their mother during pregnancy. These borrowed antibodies provide some early protection, but they fade steadily over the first 6 to 12 months of life. As they decline, your baby becomes increasingly vulnerable to infection.
There’s an added wrinkle: even low, fading levels of maternal antibodies can partially interfere with how well a vaccine works. The leftover antibodies essentially signal the baby’s immune system that protection already exists, which dampens the response to vaccination. This is one reason babies need multiple doses spaced a few weeks apart. Each dose primes the immune system a little more, building a stronger and longer-lasting response as maternal antibodies continue to clear out. Skipping or delaying the 4-month dose leaves a gap right when that borrowed protection is weakening.
Common Side Effects
Most babies are fussy for a day or two after their 4-month shots. The most typical reactions are mild and short-lived:
- DTaP: Soreness or swelling at the injection site, low fever, fussiness, fatigue, loss of appetite, and occasionally vomiting.
- Hib: Redness, warmth, and swelling where the shot was given, plus possible fever.
- PCV: Pain or tenderness at the injection site, fever, fussiness, fatigue, and loss of appetite.
- Polio: A sore spot with redness or swelling at the injection site.
- Rotavirus: Mild irritability, temporary diarrhea, or brief vomiting.
Symptoms usually resolve within two to three days. A low-grade fever in the first 24 to 48 hours is the body’s normal immune response, not a sign of illness.
When Side Effects Need Attention
Serious reactions are rare but worth knowing about. For DTaP specifically, a fever above 105°F, nonstop crying lasting three hours or more, or seizures are considered uncommon but significant reactions that need medical evaluation. For all the vaccines, signs like difficulty breathing, hives, or swelling of the face and throat could indicate an allergic reaction, which typically happens within minutes to hours of vaccination and requires immediate care.
Helping Your Baby Feel Better Afterward
Comfort nursing or bottle feeding right after the shots can help calm your baby quickly. Skin-to-skin contact, gentle rocking, and a calm environment all help too. A cool, damp cloth on the injection site can ease soreness and swelling.
If your baby develops a fever or seems especially uncomfortable, infant acetaminophen (Tylenol) is an option for babies 12 weeks and older. Dosing is based on your baby’s weight, not age. For the liquid formulation (160 mg per 5 mL), a baby weighing 12 to 17 pounds typically gets 2.5 mL, while a baby weighing 6 to 11 pounds gets 1.25 mL. Use the syringe that comes with the medicine rather than a kitchen spoon, and you can repeat the dose every 4 to 6 hours if needed, up to five times in a day. Ibuprofen is not recommended before 6 months of age.
Experts generally advise against giving acetaminophen before the appointment “just in case,” since preemptive dosing may slightly reduce the immune response. Wait to see if your baby actually needs it.
What Comes Next in the Series
The 4-month visit is the middle chapter of a busy first year. At 6 months, your baby will receive third doses of DTaP, Hib, PCV, and polio, plus the start of the annual flu vaccine. If your baby is on a three-dose rotavirus schedule, the final rotavirus dose also happens at 6 months. After that, the next major round of vaccines falls between 12 and 15 months, when the series for several of these vaccines wraps up and new ones (like measles, mumps, and rubella) begin.