• The Infant Vaccine Schedule

Infant immunization schedule: Why, what and when?

The schedule of recommended vaccines for infants can be confusing and overwhelming. As a parent, it seems as though you are always going to the doctor’s office to give your baby a vaccine. If you find yourself nodding in agreement, you may also be searching for clarity and a better understanding of the vaccine schedule, what vaccines do, and the optimum time to vaccinate yourself and your children.

Vaccines work by preparing the body to fight illness. The body practices fighting disease by making antibodies that recognize specific parts of illness-causing germs. This is called immunity.

Who recommends vaccines, and what is considered in the recommendation process?

The CDC sets the childhood immunization schedule based on recommendations from the Advisory Committee on Immunization Practices (ACIP) − made up of medical and public health experts. Among the topics discussed at each ACIP meeting are the safety and efficacy of the vaccines when given at specific ages, the severity of the vaccine-preventable diseases, and how beneficial these vaccines are to children of different ages. This schedule has to be approved by the American Academy of Pediatrics (AAP) and the American Academy of Family Physicians (AAFP).

Why are so many vaccines recommended before age 2?

Babies’ ability to mount an immune response begins before they are born. By the second trimester, a baby’s immune system has the potential to respond to large numbers of foreign antigens. They get some passive immunity from their mothers through the placenta. However, this immune system gets weaker as your baby grows, and babies don’t get protective antibodies from their mother for most vaccine-preventable diseases.

During the birthing process, a baby develops what is known as the active immune response. This helps deal with all the microbes that meets them from the world they are born into. Within the first week, the immune response gets even stronger, and breast-fed babies even get a boost from colostrum in breastmilk. Thus, the newborn baby typically has a healthy and robust, yet naïve, immune system. One could say that the newborn’s immune system needs a lot of training to sharpen the “memory” of its immune fighting cells. This memory is what protects your baby from birth and thereafter.

Vaccines given in the first 2 years of life are scheduled based on this knowledge, as this is the time children are most likely to die or have serious complications from some vaccine-preventable diseases. Depending on the vaccine, more than one dose is needed to build the best immunity or boost immunity over time.

Overall, children are exposed to fewer antigens in vaccines today than in the past. In the 1900s, a smallpox vaccine had 200 antigens. Today, for all the vaccines your child receives, the total antigen is 160. This is a “drop in the ocean,” considering your child is exposed to over 250,000 antigens once they are born. So, the vaccine schedule is designed to protect children when they are most at risk.

What are the types of vaccines?

There are four main types of vaccines:

  • Attenuated (weakened) live viruses - Measles, mumps, rubella, chickenpox vaccines
  • Killed (inactivated) virus or bacteria - Polio vaccine
  • Toxoid vaccines have an inactivated toxin produced by the bacteria - Tetanus, diptheria and whooping cough vaccines
  • Conjugate vaccines contain parts of bacteria combined with proteins - Hib

When should children get vaccinated?

Protecting your child starts before they are born. The Influenza and Whooping Cough vaccine are given to parents before a child is born. Once a baby is born, this is the recommended vaccine schedule:


  • Hepatitis B

2 months

  • Whooping Cough, Diphtheria, Tetanus
  • Hib, PCV (meningitis)
  • Rotavirus
  • Hepatitis B
  • Polio

4 months

  • Whooping Cough, Diphtheria, Tetanus
  • Hib, PCV
  • Rotavirus
  • Polio

6 months

  • Whooping Cough, Diphtheria, Tetanus
  • Hib, PCV
  • Rotavirus (a third dose may be needed depending on brand of vaccine used)
  • Hepatitis B
  • Polio

12-15 months

  • Measles, Mumps, Rubella
  • Chickenpox
  • Hepatitis A (2 doses given 6 months apart)
  • Polio

15-18 months

  • Whooping Cough, Diphtheria, Tetanus
  • Hib, PCV
  • Hepatitis A

What about an alternative vaccine schedule?

Children respond to multiple vaccines in a manner similar to individual vaccines. Vaccines do not overload the immune system. Spreading out shots leaves your child at risk of getting a vaccine-preventable disease. Parents who are concerned can reduce the number given at a visit by using the flexibility built into the current CDC immunization schedule.

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Adwoa Osei, MD, is a board-certified pediatrician at UCR Health. To learn more, view Dr. Adwoa Osei’s profile.