In medicine, a conjugate vaccine, or conjugated vaccine, is a type of vaccine that is created by joining an antigen to a protein molecule. Conjugated vaccines are usually used to immunize babies and children against certain bacterial infections. The immature immune systems of very young people often have difficulty recognizing certain antigens, so ordinary vaccines may not be effective for some diseases. The protein part of this vaccine acts as a carrier for the antigen, and serves to magnify the immunological response to it. In this way, a conjugate vaccine may be significantly more successful in immunizing babies and children against certain bacteria.
The types of bacteria these vaccines are designed to inoculate children against tend to be bacteria that have polysaccharide capsules. In these bacteria, a layer of mucus constructed from polysaccharide molecules protects the antigens on the surface of the bacterial cell. This makes it more difficult for human immune cells, or white blood cells, to recognize the bacteria and mount an immunological attack. A conjugate vaccine, therefore, usually consists of a polysaccharide antigen combined with a carrier protein. The combination of the antigen with the protein creates a substance that is more easily recognizable to the white blood cells in the human blood, resulting in a stronger immune response.
Two important vaccines in child health care are the pneumococcal conjugate vaccine (PCV) and the meningococcal conjugate vaccine (MCV). PCV is routinely used in many countries to prevent bacterial meningitis, pneumonia, and related infections in children. This vaccine does not protect immunized children against all pneumococcal bacteria. There are over 90 different kinds of pneumococcal bacteria, and the pneumococcal conjugate vaccine only protects against seven of these. These seven types of bacteria, however, cause a large proportion of severe pneumococcal diseases, and the vaccine can help prevent a great majority of these infections.
The meningococcal vaccine is designed to protect children against a different strain of meningitis, which is caused by a bacterium called meningococcus. It works in a similar way to PCV and is used to immunize both young children and adolescents up to 18 years old. This vaccine is typically administered to children and young adults who have experienced exposure to a meningococcal strain of bacteria, for example if an incidence of meningitis has occurred in a school or college.