can interfere with growth of the vaccine organism and lead to a poor response or no response to the vaccine (also known as vaccine failure). Measles vaccine virus seems to be most sensitive to circulating antibody. Polio and rotavirus vaccine viruses are least affected. Live attenuated vaccines are labile, and can be damaged or destroyed by heat and light. They must be handled and stored carefully. Currently available live attenuated viral vaccines include measles, mumps, rubella,  varicella, yellow fever, influenza (intranasal) and Oral polio vaccine. Live attenuated bacterial vaccines include BCG and oral typhoid vaccine. Inactivated vaccines These vaccines are produced by growing the bacteria or virus in culture media, then inactivating it with heat and/or chemicals (usually formalin). In the case of fractional vaccines, the organism is further treated to purify only those components to be included in the vaccine (e.g., the polysaccharide capsule of pneumococcus). Inactivated vaccines are not alive and cannot replicate. The entire dose of antigen is administered in the injection. These vaccines cannot cause disease from infection, even in an immunodeficient person. Unlike live antigens, inactivated antigens are usually not affected by circulating antibody. Inactivated vaccines may be given when antibody is present in the blood (e.g., in infancy, or following receipt of antibody-containing blood products). Inactivated vaccines always require multiple doses. In general, the first dose does not produce protective immunity, but only "primes" the immune system. A protective immune response develops after the second or third dose. In contrast to live vaccines, in