Current Controversies in the USA Regarding Vaccine Safety

Archana Chatterjee; Catherine O'Keefe

Disclosures

Expert Rev Vaccines. 2010;9(5):497-502. 

In This Article

An Overwhelmed or Healthy Immune System?

The number of recommended childhood vaccines has increased exponentially in the last 50 years. A fully immunized child by the age of 2 years will have received 14 different vaccines and up to 26 injections. Some healthcare visits may require five injections at a single visit. Understandably, parents have voiced concern about too many vaccines overloading or weakening the fragile immune system of their infant.[46] This notion may be based upon reports that certain live viral vaccines, such as those containing attenuated measles virus, can cause a decrease in protective immune responses to varicella vaccine[47] and that the high-titered measles vaccine (Edmonston–Zagreb strain) can cause an excess of cases of invasive bacterial infections in developing countries.[48] It should be noted that current vaccines (including the highly attenuated Moraten strain of measles vaccine) do not appear to cause clinically relevant immunosuppression in healthy children.[3]

The neonate's immune system begins to develop and is primed in utero.[49] There is evidence that fetuses have the capacity to form antibodies in the presence of intrauterine infections.[50] Infants can generate functional T cells as well as the full range of B-cell responses.[51] Continued maturation of the immune system is observed as the neonate, within hours of life, begins to colonize his/her intestinal tract and respond to a whole host of environmental antigenic stimuli. Infants in fact have an amazing capacity to respond to a vast array of antigens, including vaccines. However, the infant's immune system is not capable of responding with adult efficiency. Maturation of the immune response occurs in an orderly fashion from approximately 16 weeks gestation and slowly gains momentum in the first year of life. This, along with the presence of maternal antibodies provided passively, may account for the need for multiple injections to complete the primary series of several vaccines.[49,50] Data suggest that, theoretically, the intact immune system could respond to 109–1011 different antigens.[51] Today's vaccines contain far fewer antigens than the immune system is designed to respond to. Medical advances in vaccinology have contributed to the decline in the number of antigens in modern vaccines. For example, the whole-cell pertussis vaccine contained approximately 3000 proteins compared with the two to five proteins found in the current acellular pertussis vaccines.[51]

Thus, parents and caregivers should be reassured based on these data that vaccines will not overwhelm or weaken the infant immune system.

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