STOP Transmission of Polio (STOP) nurse administering an oral polio vaccine to a child under 5 years of age, during a National Immunization Day (NID) in Uttar Pradesh, nothern India. Thousands of children throughout the country receive a polio vaccine on each NID. Since its inception in the fall of 1998, the STOP Transmission of Polio (STOP) immunization initiative teams have worked in over 50 countries. In the first years of the program, most STOP team members worked primarily to bolster acute flaccid paralysis (AFP) surveillance, support national immunization days, and conduct polio case investigation and follow-up. There are two kinds of polio vaccine: IPV, which is a shot given in the leg or arm, depending on age, which is recommended in the United States today, and a live, oral polio vaccine, or OPV, (drops that are swallowed). In the case of children, IPV may be given at the same time as other vaccines. Most people should receive a polio vaccine when they are children. Until recently OPV was recommended for most children in the United States. Both vaccines give immunity to polio, but OPV is better at keeping the disease from spreading to other people. However, for a few people (about one in 2.4 million), OPV actually causes polio. Since the risk of getting polio in the United States is now extremely low, experts believe that using oral polio vaccine is no longer worth the slight risk, except in limited circumstances which your doctor can describe. The polio shot (IPV) does not cause polio. The poliovirus, an enterovirus, enters through the mouth, and primary multiplication of the virus occurs at the site of implantation in the pharynx and gastrointestinal tract. The virus is usually present in the throat and in the stool before the onset of illness. One week after onset there is little virus in the throat, but virus continues to be excreted in the stool for several weeks. The virus invades local lymphoid tissue, enters the blood stream, and then may infect cel