Future Considerations and Concerns
_____________________________________________________________________________________________________________

[Back to Table of Contents]

Thanks to years of cross platform cooperation between researchers, governing bodies, financial institutions, and substantial community participation, two general forms of vaccines have been implemented to effect a considerable interruption in the transmission of polio in the Americas. Polio-free zones are currently present or emerging in the Americas, northern, southern, and eastern Africa, the Arabian Peninsula, Western and Central Europe, and the Western Pacific. Yet as encouraging as these facts may seem, several threats still exist that can easily bring about another polio epidemic.

1.  Reversion
The oral polio vaccine developed by Sabin uses an attenutated poliovirus developed via serial passage selection through monkey kidney cells in the US and human fibroblasts elsewhere.  The attenuated poliovirus, however, can still revert to the virulent form either via back mutation to the virulent wild type form or recombination with other types to re-attain the necessary gene sequence to produce the internal ribosome entry site (IRES) necessary for infection and manifestation into disease.

2.  Vaccinees as healthy carriers
A vaccinated person, whose attenuated poliovirus has reverted, will appear healthy for nearly 30 days due to the incubation period which can last for as long as 35 days.  During that period, the person can spread the reverted poliovirus either fecally or orally without exhibiting any symptoms of polio and thus transforming him into a "healthy carrier."

3.  Potential Hot-zonesDespite substantial progress, paralytic polio remains highly endemic throughout the India subcontinent and continues to thrive in sub-Saharan Africa, Asia, and several republics of the former Soviet Union.Poor sanitation, crowding, lack of routine vaccination, and pockets of unvaccinated children contribute to the persistence of polio in these areas.  With the high rate of intercontinental travel, these reservoirs of polio still present a high risk to the polio-free western world.

The Future of Poliovirus Vaccines

IPV is appropriate for combination with other vaccines such as DTP, reducing the number of injections required for children. Neutralizing antibodies can be induced by viral proteins alone, opening up the possibility of the use of subunit poliovirus vaccines with the use of recombinant DNA and synthetic antigen. The ability of poliovirus to exploit M cell transport to cross the mucosal epithelium make it an excellent candidate oral vaccine vector for delivering foreign antigens as a live vaccine or as virus-like particles. Wild type and attenuated poliovirus have been used as vaccine vectors to express a variety of antigens such as HIV-nef, HIVp17 and p24, gag fusion protein, and a segment of Influenza A Hemagglutinin. 
Future plan for accelerated eradication of poliomyelitis
Development of improved methods for identifying wild-type poliovirus and determining infection with poliovirus:

1.PCR technique for identifying wild-type poliovirus in clinical specimens and
environmental samples.

2.Nucleic acid hybridization to specifically identify all wild-type polioviruses.

3.Restriction fragments length polymorphism (RFLP).

4.Use of mouse cell lines expressing the human poliovirus receptor.

5.Use of Sabin-specific monoclonal antibodies for rapid identification of Sabin-related
poliovirus by neutralisation.

6.Development of a standard test for detection of poliovirus-specific IgM antibodies to evaluate transgenic mice as an animal model for neurovirulence test of oral poliomyelitis vaccine.

http://www.who.org/vaccines-diseases/research/virus1.htm

[Back to Table of Contents]