These inactivated vaccines do not cause disease in people who receive them, but they can stimulate the immune system. Such vaccines in use today include those against polio and influenza. Subunit Vaccines . Recent research has focused on developing vaccines that use only part of the bacterium or virus. These vaccines, called subunit vaccines, produce an effective immune response without stirring up separate and potentially harmful immune reactions to the many antigens carried on a microbe.
Subunit vaccines are currently available for typhoid, and hepatitis b.
An acellular pertussis subunit vaccine has been demonstrated to be effective in preventing whopping cough in babies and young children. Although not considered subunit vaccines, vaccine candidates using only the outer polysaccharide coat of the bacterium have been developed for meningitis and pneumonia. Conjugate Vaccines . Bacterial diseases such as pneumonia and meningitis once caused considerable illness and death among babies and children in the United States. Bacteria that cause these diseases have an outer coat that cannot be recognized by the immature immune systems of young infants and, therefore, vaccines made from these bacteria are not effective in babies.