We know it’s painful to watch baby get poked and even worse to hear the inevitable crying, but immunizations are crucial for their health. If your baby is extremely sick, then your pediatrician will probably modify the immunization schedule. Otherwise, your baby should get vaccinated on a regular basis.

Though some children do suffer from mild reactions to immunizations, very few become seriously ill, and any pediatrician will reassure you that the benefits of having antibodies (needed to fight infections) far outweigh the risks of getting shots. So what exactly do these shots protect your baby from? A breakdown, with help from the American Academy of Pediatrics:

Hepatitis B Vaccine (HepB)

It prevents: Hepatitis B, a chronic or acute liver disease that can lead to liver failure and cancer.

When baby gets it: The first dose should be given before she’s discharged from the hospital after birth. A second dose should happen between 1 and 2 months of age. If, for some reason, baby doesn’t get the hepatitis B vaccine at the hospital, she’ll need three doses — at 0, 1 and 6 months — and the final dosage should be administered no earlier than 24 weeks old.

If mom is hepatitis B surface antigen (HBsAg) positive, baby should get the vaccine — plus hepatitis B immune globulin — within 12 hours of birth, and then receive three more doses of the vaccine between 9 and 18 months, and be tested for HBsAg and the antibody to HBsAg one to two months after completion of the dosages.

Possible side effects: Brief soreness and fussiness.

Rotavirus Vaccine (RV)

It prevents: Rotavirus, the most common cause of diarrhea and vomiting in infants and young children, which can cause severe dehydration in babies. It’s not a shot — this vaccine is taken orally.

When baby gets it: Between 2 months and 4 months of age, in two to three doses, depending on the brand of vaccine. He may also need another dose at 6 months, so double-check with your doctor.

Possible side effects: Fussiness, and some babies may have mild, temporary diarrhea or may vomit.

Diphtheria and Tetanus Toxoids and Acellular Pertussis Vaccine (DTaP)

It prevents: A combination vaccine to protect against diphtheria, tetanus and pertussis. Diphtheria used to be a major cause of childhood illness and death. Now, it only occurs in a few cases a year, thanks to this vaccine. Tetanus is a serious illness that causes painful tightening of the jaw muscles. Pertussis is also known as the whooping cough, a highly contagious respiratory infection.

When baby gets it: At 2 months, 4 months and 6 months, and between 15 and 18 months and 4 to 6 years.

Possible side effects: Tenderness, swelling, redness, fever, loss of appetite within two days of receiving the shot.

Haemophilus Influenzae Type B Conjugate Vaccine (Hib)

It prevents: “Hib” disease, which you probably haven’t heard of, but it’s very harmful. Hib was the leading cause of bacterial meningitis in children before the vaccine was developed. Kids with Hib may suffer permanent brain damage or have serious complications, like pneumonia.

When baby gets it: At 2 months, 4 months and 6 months, and between 12 and 15 months.

Possible side effects: Fever, redness and/or tenderness at the site of the shot.