Crunching the Vaccine Numbers
World Mercury Project gets questions about the number of vaccines given to young children in America today. Different articles cite different numbers and the totals can be confusing. This article and chart are designed to clarify the vaccine schedule and explain why the numbers may not always “add up.” To be accurate, wording about total numbers of vaccines should include phrases like, “may receive up to” or “typically” or “between X and Y” number of vaccines. The individual numbers for any given child will vary depending on the specific vaccines used in his pediatrician’s practice or clinic.
To start, there is a difference between the number of vaccines given and the number of antigens given. According to the National Cancer Institute, an antigen is:
Any substance that causes the body to make an immune response against that substance. Antigens include toxins, chemicals, bacteria, viruses, or other substances that come from outside the body. Body tissues and cells, including cancer cells, also have antigens on them that can cause an immune response. These antigens can also be used as markers in laboratory tests to identify those tissues or cells.
In any given vaccine, there will be one or more antigens. A vaccine that contains only one antigen is called monovalent. Examples include the Hiberix, ActHib and PedvaxHib vaccines, each of which contains a single antigen for Haemophilus influenzae type b, a bacterium that can cause meningitis. This single antigen can also, however, be combined into a polyvalent (or multivalent) vaccine such as Pentacel which adds antigens for diphtheria, tetanus, acellular pertussis and inactivated polio; Pentacel contains five antigens in total, hence its name.
A polyvalent or multivalent vaccine can either contain multiple antigens for different diseases (as with Pentacel) or it can contain multiple antigens for different strains or serotypes of the same disease. An example of this would be Pneumovax 23 which contains antigens for 23 different serotypes of pneumococcal bacteria. Annual influenza vaccines can be either trivalent (three strains) or quadrivalent (four strains). The Centers for Disease Control (CDC) and the World Health Organization (WHO) determine the different strains included in the vaccines each flu season based on the strains that are circulating internationally.