Inactivated Poliovirus Vaccine
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Salk Inactivated Polio Vaccine (IPV)
Poliomyelitis control was made possible when, in 1949, American bacteriologist John Franklin Enders and his coworkers discovered a method of growing the viruses on tissue in the laboratory. American physician and epidemiologist Jonas Salk used this technique to develop a vaccine prepared from inactivated poliomyelitis viruses of the three known types. The vaccine was pronounced safe and effective in 1954 and licensed in1955. An enhanced-potency IPV (e-IPV) was licensed in November 1987, and first became available in 1988 e-IPV. IPV is manufactured by Connaught Laboratories Ltd. (Willowdale, Ontario, Canada). The Salk-type inactivated poliovirus vaccine (IPV) consists of a mixture of three poliovirus serotypes (trivalent) grown in monkey kidney cell cultures (Vero cell line) and are inactivated by 37% formaldehyde (formalin) treatment. Two enhanced forms of inactivated poliovirus vaccine are currently licensed in the United States, but only one vaccine (IPOL, Pasteur Merieux Connaught) is actually distributed. It is given in a single dose prefilled syringe and should be administered by subcutaneous injection. Its effectiveness depends on stimulation of serum (blood) neutralizing antibodies that block the spread of poliovirus to the central nervous system. It has some suppressive effect on replication of wild poliovirus in the highly vascularized oropharyngeal region, but it has no effect on replication in the gut or on viral transmission in the stool. As a result, it provides individual protection against polio paralysis but, unlike OPV, cannot prevent the spread of wild poliovirus. The vaccine contains 2-phenoxyethanol, and trace amounts of neomycin, streptomycin, and polymyxin B.

Enhanced Inactivated Poliovirus Vaccine (E-IPV)

Vaccination with E-IPV an inactivated polio vaccine with increased antigenic content, results in higher seroconversion rates(up to 100%) and higher serum antibody levels than OPV. Two doses of E-IPV are highly immunogenic and clinically effective. However, E-IPV induces nearly the same degree of intestinal immunity as ealier IPV preparations despite higher potency and superiority in inducing a humoral antibody response.

Cost

E-IPV enables children to be protected against the six diseases of the Expanded Programme on Immunization in only 2 visits. The costs of vaccination would be roughly halved. The United Nationís Childrenís Fund estimates that the cost of completely immunizing a child is about $5 US. The cost of producing an inactivated vaccine is much higher than that of a live vaccine. The cost of the actual vaccine is about 10% of that value, or $0.50. E-IPV could be offered at a price of $0.45US per dose. The total cost of a immunization against all six diseases would be about $1.05. Analysis has shown that the cost of one complete immunization would cost around $3.07, slightly more than half of the cost when OPV is administered.
Advantages
IPV does not contain live poliovirus. Consequently, immunization with IPV carries no risk of vaccine-associated polio paralysis (VAPP). Immunization with IPV triggers an excellent systemic immune response to poliovirus and protects well against paralytic poliomyelitis in most recipients. While a single dose of IPV produces little or no immunity, 90% or more of vaccine recipients develop protective antibody to all 3 poliovirus types after 2 doses, and almost 100% are immune following 3 doses. 

Disadvantages
Unlike the oral vaccine, IPV confers very little mucosal immunity. IPV is more expensive than OPV (nearly five times the price). The reliance on syringes and the need for trained health workers to administer the vaccine using sterile injection procedures also add to the inconveniences of using IPV in developing countries with endemic poliomyelitis. Although minor local reactions such as redness and pain may occur following administration, no serious adverse reactions have been reported. Allergic reactions to trace amounts of streptomycin, polymyxin B, and neomycin, may occur as well. Persons who receive IPV are more readily infected with wild poliovirus than OPV recipients. A person who received IPV could become infected with wild poliovirus in an endemic area and could be shedding wild virus upon return to the United States. The infected person would be protected from paralytic polio, but the wild virus being shed in the stool could spread and result in transmission to a contact. The duration of immunity to IPV is not known with certainty, although it probably provides protection for many years after a complete series. When a person immunized with IPV is infected with wild poliovirus, virus can still multiply inside the intestines and be shed in stools -- risking continued circulation. For this reason, OPV is used wherever a polio outbreak needs to be contained, even in countries that rely exclusively on IPV for their routine immunization program, for example during the polio outbreak in the Netherlands in 1992.


 
Advantages
Disadvantages
Salk Vaccine (IPV)
a. Cannot undergo genetic mutation to increase virulence
a. Fails to elicit gut immunity
b. Maintains potency without refrigeration
b. Response parenteral administration (injection)
c. Overall vaccine distribution may become cheaper if E-IPV is combined with DTP vaccine.
c. Vaccine is expensive (see advantages, point c)
d. Some of the lots have inadequate antigenic potency
e. Confers immunity only after four boosters (Older IPV)
f. Stringent contorl of production required to ensure inactivation

 

IPV Seroconversion rates better in developing world than OPV

There are about 200,000 cases per year of poliomyelitis in the developing world. OPV efficency against PV types one and three are lower than expected in the developing world. Vaccine instability, vaccine formulation, breast feeding, malnutrition, and inhibitive substances in intestines have been implicated in contributing to the reduced efficacy of OPV. One of the main factors associated with the lack of seroconversion was a concurrent infection with a nonpolio enterovirus. IPV has proven to be superior to OPV in developing countries.

 



 
Country
Vaccine
No. of Doses
% with Antibody
Type 1
Type 2
Type 3
Brazil
IPV
2
99
100
100
IPV
3
100
100
100
Mali
IPV
2
100
100
100
India
IPV
2
100
100
100
Bravil
OPV
2
77
95
79
OPV
3
84
98
91
Mali
OPV
2
49
77
77
India
OPV
3
69
90
76

Taken from Beale, A. J.ÝEfficacy and Safety of oral poliovirus vaccine and inactivated poliovirus vaccine.Ý The Pediatric Infectious Disease Journal.Ý1991;10(12):971

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