Problem With Polio vaccine

• The World Health Organization has given countries two weeks to replace a problem polio vaccine blamed for some outbreaks of the crippling disease.
• The live polio virus used in some vaccines is one of the biggest obstacles to eradicating the disease. The wild version of the virus now exists only in Afghanistan and Pakistan, but a type of vaccine that contains small amounts of weakened but live polio still causes occasional outbreaks elsewhere.
• There is concern regarding OPV because Oral polio vaccine (OPV) replicates in the gut and can be passed to others through faecal-contaminated water.
• WHO recommends that the OPV should be phased out worldwide and replaced by the inactivated polio vaccine (IPV).

About OPV (oral polio vaccine)
OPV was developed in 1960 by Dr. Albert Sabin. It consists of live polioviruses attenuated by extensive passage of the original wild-type stains of poliovirus in cell cultures or in monkeys in vivo. This results in mutation of the virus, which weakens its potential to cause paralysis, while maintaining the antigenity by inducing the production of antibodies by the immune systems of the human body.
The advantages of OPV are as follows:

• OPV can protect children against paralysis once infected as well as limit the spread of wild virus among their contacts because OPV induces both serum immunity and intestinal immunity. Intestinal immunity limits the multiplication of wild virus inside the gut and thus reduces fecal excretion (hence possible transmission) of the wild virus.
• OPV can be delivered with low cost, firstly because the price is lower than that of IPV, secondly because OPV is administered orally, and thus the vaccination does not need professionally trained health workers and injection-related supplies (e.g., syringes).
• OPV is delivered orally, so unsafe injection is not an issue.

The disadvantages of OPV are as follows:

• It can cause vaccine-associated paralytic poliomyelitis (VAPP), although the probability is very low (1 case per 2.5 million doses), because some people are sensitive to vaccine virus, especially those who are immunodeficient.
• OPV may be less potent than IPV in inducing serum immunity in developing countries, where the infection of the intestines by other viruses may prohibit the intake of OPV. Thus it often needs repeated vaccination of up to five to 10 doses to protect all children). Tese kinds of limitations to OPV were particularly reported in India and Africa

About IPV
IPV was developed in 1955 by Dr. Jonas Salk. IPV is delivered via injection.
The advantages of IPV :

• It can effectively protect individual children against paralysis after three doses with a protection rate of nearly 100 percent.
• It does not cause VAPP because the vaccine consists of killed poliovirus.
• IPV can be combined with other injectable vaccines (such as DTP and Hib) to reduce the cost of administration and increase immunization coverage.

The disadvantages of IPV are as follows:

• IPV only induces serum immunity, not intestinal immunity. Thus, IPV vaccination can effectively protect the vaccinated individuals against paralysis, but does not readily protect all of them against infection with the wild virus. If vaccinated children are infected, they can become a source of infection by wild virus if their antibody levels are not high enough to stop virus excretion.
• The cost of IPV vaccination is higher than OPV because its price is higher and it requires injections by trained health workers.
• Wild poliovirus could escape from the production process.
• There is a risk of unsafe injections, which can lead to transmission of blood-borne diseases.

By: Vishal