Poliovirus Vaccine: Salk and sabin vaccine

Two types of vaccine are available against poliomyelitis, inactivated vaccine (IPV, Salk) and live attenuated oral vaccine (OPV, Sabin). Both vaccine formulations contain all three polio types.

Oral Polio Vaccine (OPV) /Sabin 
OPV was the most widely used vaccine for prevention of poliomyelitis. It is composed of attenuated strains of the three poliovirus types, and is administered orally.
It has been instrumental nearly eradicating the virus from the planet. Lately, WHO has recommended replacement of  OPV by inactivated poliovirus vaccine (IPV) as scientist finds the evidences of reversion to virulence in OPV strains.
At least two or three doses are considered necessary to ensure adequate immunity, in some countries even five to six or more doses are given in the primary course. Revaccination is used to a varying degree. A full primary course induces an antibody response against all three types in more than 90% of vaccinees and gives a high degree of protection against disease.

OPV also induces intestinal immunity due to production of secretory IgA antibodies. This is important for inhibition of virus replication in the gut, diminishing the possible spread of virus to susceptible contacts. OPV is almost non-reactogenic, and is very safe. However, in a few cases an attenuated vaccine strain may induce paralytic disease. This occurs in about one case per 1–10 million vaccine doses administered.

inactivated poliovirus vaccine (IPV)
IPV was the first vaccine used against poliomyelitis. It contains the three types of poliovirus inactivated by formaldehyde and is administered parenterally. The use of IPV in the late 1950s was followed by a 90% reduction of poliomyelitis cases when it was replaced in many countries by the more easily administered OPV around 1960. Newer IPVs have higher immunogenic potency which has led to a reintroduction of IPV in many developed and developing countries.
The primary vaccination course with IPV consists of two or three doses, usually followed by revaccination after intervals of about 5–10 years during childhood and adolescence. Some countries are using a combination of OPV and IPV.
Passive immunization is of little value.
Salk killed vaccine
– viral pools of adequate titer filtered and inactivated with formalin (1:4000) 370C / 12-15 days.
–         given by injection, IPV
–         3 doses given 4-6 weeks apart + booster 6 months later.
1st dose to babies after age of 6 months.
Sabin live vaccine ( OPV).
–         developed by plaque selection in monkey kidney tissue culture on HDCC.
–         Stringent precautions to be taken to ensure freedom from extraneous agents like SV40 and B- virus.
–         Issued either in monovalent or trivalent form; 3 doses at 4-8 weeks interval.
–         Vaccine stabilized by MgCl2; shelf life at 4-80C is 4 monts and at -200C is 2 yrs.
–         Improper storage conditions and cold chain failure partly responsible for apparent failure of OPV.
–         Live vaccines infects, multiplies and disseminated in the community.
–         Produces not only IgM and IgG but also IgA in the intestine, and then becomes resistant to re- infection.
o       Both killed and live vaccines protect the CNS, but gut develops a far increased degree of resistance after administration of live – virus vaccine.
o       OPV not safe in immunodeficient or immuno- suppressed subjects.
o       Interference → if alimentary tract of a child infected with another enterovirus at the time vaccine is given, establishment of polio infection and immunity may be blocked.
o       Frequent diarrhoeal diseases prevent colonization by vaccine virus.
o       Breast feeding immediately before or after vaccine may neutralize the vaccine virus.
o       IG provides protection for a few weeks against paralytic disease, but doesn’t prevent subclinical infection.
o       Effective only if given shortly before infection; no value after clinical symptoms develop.

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