Sabin live attenuated Oral Poliovirus Vaccine (OPV)
In 1961, type 1 and 2 monovalent oral poliovirus vaccine (MOPV) was licensed, and in 1962, type 3 MOPV was licensed. In 1963, trivalent oral poliovirus vaccine (OPV) was licensed and largely replaced IPV use. OPV is manufactured by Lederle Laboratories Division, American Cynamid Company (Pearle River, NY). Trivalent OPV contains live attenuated strains of all three serotypes of poliovirus in a 10:1:3 ratio. The viruses were attenuated by serial passage in monkey kidney, Vero, or human diploid fibroblast cell cultures, allowing it to accumulate mutations. Ultimately, this resulted in an attenuated virus that could be given to a patient orally. The weaker virus replicates normally in the intestine, but cannot grow well enough to invade the central nervous system. The vaccine is supplied as a single 0.5 ml dose in a plastic dispenser. The vaccine contains trace amounts of streptomycin and neomycin. The vaccine potency is stabilized with molar magnesium chloride or sucrose. OPV replicates in the ororpharyngeal and gastrointestinal tract and in lymph nodes that drain the intestine. OPV induces two separate immune responses. First, OPV activates the humoral immune response, prompting the production of serum-neutralizing antibodies in the blood to all three polio serotypes. This systemic response is long lasting and helps to prevent the spread of poliovirus to the nervous system. OPV also produces a mucosal immune response consisting of interferon and virus-specific IgA antibody in the epithelial lining of the ororpharyngeal and gastrointestinal tract. Only primates are susceptible to all three serotypes of poliovirus, so the safety of oral poliovirus vaccine (OPV) and its consistency have been tested in the monkey neurovirulence test (MNVT). About 100 monkeys are used for each trivalent vaccine batch. In a number of countries, the MNVT is performed twice, once by the manufacturer and once by the national control authority. In addition to the high cost, monkeys are usually obtained from the wild with a potential for transmitting exotic diseases to humans. An alternative animal system being evaluated is susceptible transgenic mice expressing the human poliovirus receptor. 

Advantages
OPV is given orally rather than by injection. Its administration does not require a trained health worker and sterile injection equipment. At a current price of 8 US cents a dose, the vaccine is relatively inexpensive, facilitating mass purchasing of the vaccine during National Immunization Days. Short-term shedding of OPV in the stools of recently immunized persons can result in the passive immunization of persons within close contact. OPV is highly effective in producing immunity to poliovirus. A single dose of OPV produces immunity to all three vaccine viruses in about 50% of recipients. Three doses produces immunity to all 3 poliovirus types in more than 95% of recipients. Immunity from oral poliovirus vaccine is probably life long. OPVís ability to stimulate mucosal immunity is responsible for the success of OPV mass campaigns in interrupting wild poliovirus transmission. Therefore, OPV remains the vaccine of choice for the eradication of polio. OPV intestinal immunity reduces the chance that a vaccinated person will become infected with wild virus if he or she is exposed while visiting a polio endemic country. 

Disadvantages
The greatest concern with the use of live attenuated vaccines is their potential for reversion to neurovirulence. All three OPV vaccine strains show some tendency to revert to neurovirulence. Sabin types 2 and 3 vaccine viruses revert more easily to neurovirulence phenotypes as compared to type 1. However, none of the serotypes are genetically unstable. Single-base mutations that are strongly associated with attenuation and reversion to neurovirulence have been identified. Major attenuating mutations for all three serotypes have been identified in the 5p non-coding region (NCR), at position 480 for type 1, 481 for type 2, and 472 for type 3. For type 3, an additional point mutation associated with both attenuation and temperature sensitivity has been identified at position 2034 in theVP3 capsid gene. The three serotypes of OPV are relatively unstable during passage in cell culture and have been found to be unstable and rapidly lost during replication in the human gastrointestinal tract. Vaccination with OPV results in the release of a variety of live mutant viruses in the feces. Despite the excellent safety record of OPV, in approximately 1 in every 3 million doses of the vaccine, the live attenuated vaccine virus in OPV can cause paralysis in the vaccinated child or in a close contact. This extremely low risk of vaccine-associated polio (VAPP) is accepted by most public health programs in the world because hundreds of thousands of children would be crippled every year without OPV. Another pathogen may be acting in synchrony with polio to suppress the immune system enough to allow the mutant viruses to enter the nervous system. Temperature instability of a live virus vaccine is also a major factor. However, OPV is able to be stabilized within a solution of magnesium chloride. OPV in MgCl₂ is stable for at least twelve months at 4C, six weeks at 25C, and sufficiently immunogenic to use after one week at 37C.
 
 

Advantages	Disadvantages
Sabin Vaccine (OPV)
a. Relatively inexpensive and easily administrated	a. Can mutate to more virulent strain
b. Induces both systemic and local immunity	b. Less reliable in tropical areas (see MgCl2 discussion)
c. Prepared in human cells eliminating risk of latnet viruses found in monkey      kidney cells
d. Induces herd immunity