Polio or poliomyelitis is a viral illness that leads to paralysis or even death. The poliovirus is communicable and generally spreads from drinking water contaminated from the virus; it can also spread due to close contact with an infected person. The discovery of the polio vaccine (circa 1950) has greatly reduced the incidence of this disease especially in America and Europe.
There are two main types of the polio vaccine, which work towards controlling and eliminating the spread of poliomyelitis- Inactivated Polio Vaccine (IPV) and Oral Polio Vaccine (OPV).
IPV or the Salk vaccine: It is a killed vaccine (developed by Dr. Jonas Salk in 1952) that is administered subcutaneously through an injection and contains strains of all 3 types of the virus: Mahoney (type1), MEF (type 2), and Saukett (type 3). IPV, which is grown in a monkey kidney culture and deactivated, using formaldehyde, causes serum immunity to all 3 forms of the virus; it produces antibodies in the blood. This blocks the spread of the virus to the nervous system and prevents paralysis. This immunity is at least prolonged, if not life long. However, the level of immunity evoked by IPV (including the enhanced IPV) is lower than that induced by OPV. Therefore, in this sense it is a less steadfast option. Nonetheless, the effectiveness of this vaccine has been seen in many nations like Sweden, Denmark, Finland, and Iceland.
Effects: As it contains a killed virus, this polio vaccine is easier to manage than its oral counterpart. Moreover, this is also responsible for the elimination of VAPP (Vaccine Associated Polio Paralysis). The Salk vaccine is free from any severe adverse effects. However, it provides low immunity from the wild poliovirus in the intestinal tract and is considerably more expensive than OPV.
OPV: Developed in 1958 by Dr. Albert Sabin, it contains live attenuated strains of the three aforementioned types of the poliovirus; OPV is administered at sub-physiological temperatures. The most common trivalent form of this polio vaccine effectively immunizes (often life long) an individual from all known forms of the virus especially those affecting the gastro-intestinal tract (most active site of the poliovirus). Boosters of OPV are required to achieve this. Similarly, immunity is induced to the third strain with the third booster. The vaccine contains small amounts of antibiotics—neomycin and streptomycin and it has been successful in producing antibodies in 95% of the recipients.
Effects: However, a strong correlation has been established between OPV and Vaccine Associated Polio Paralysis, which is absent in case of IPV. Moreover, especially in the U.S. the incidence of the wild type virus is so low that IPV has been favoured over OPV. OPV is recommended for countries with a low vaccination rate.
The new proposed method of polio immunization involves sequential use of IPV (first two doses) followed by OPV (doses 3 and 4). IPV induces sufficient immunity to prevent VAPP while OPV will induce optimal intestinal immunity and sustain immunity evoked by IPV.
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