diseases. >> so just what is a vaccine? >> in a weakened form that doesn't make you sick. into producing antibodies to give you immunity to a disease without ever having it in the first place. preventing disease before it occurs as showing it in the fight against polio. vaccines are effective, safe and incredibly important. and a list of vaccine preventable diseases is long. hepatitis b, measles, mumps, pneumonia, polio, rue bell la, tetanus and more. vaccines that have prevented deaths worldwide. >> this is house to house, polio campaign. >> but science often loses the argument to ideology. and that was the case in nigeria.