Polio, an infectious disease currently endemic in Pakistan and Afghanistan, is set to be eradicated by a new public health initiative by the World Health Organisation. They hope that switching the type of vaccination used will achieve this goal by 2018. It is estimated that 70% of polio infections are asymptomatic, but that 0.5% of cases will result in muscle weakness causing an inability to move and possible death.
The first effective polio vaccine was developed in 1952 by Jonas Salk and is known as the inactivated poliovirus vaccine (IPV). The IPV was introduced to the market in 1955 and is administered by injection. A second vaccine, the oral poliovirus vaccine (OPV), was developed at a similar time to the IPV. The OPV was established by Albert Sabin and was licensed for use in 1961. Together, these vaccines have reduced the total number of cases of polio from 350,000 in 1988 to 329 in 2014! If this vaccination programme is successful, polio will be only the second human disease to become extinct in history, since the eradication of smallpox in 1980.
Three types of polio are currently vaccinated against: Type 1, 2 and 3, but Type 2 has had no cases of transmission since 1999 and it is considered the weaker strain. The risk of contracting a ‘vaccine-derived’ strain of the virus outweighs the benefit of protecting against a ‘wild’ form with a small risk of infection. From mid-April to the beginning of May, 150 nations will switch their immunisation programme to a bivalent vaccination, protecting against Type 1 and Type 3 polio. The new bivalent vaccines should eliminate health risks associated with traditional vaccinations, and are based upon the OPV vaccine. However, OPV vaccines, in general, are being phased out in favour of IPV vaccines. This is hoped to completely eliminate the risk of contracting vaccine-derived Type 2 polio.
However, this news comes at a time when Yellow fever is once again becoming prominent in the African state of Angola. The mosquito-borne virus was initially reduced to areas of jungle after a highly effective species eradication regimen of Aedes aegypti and a vaccination scheme. However, due to curtailments in the control programme, mosquito populations are on the increase in several cities, where the vast majority of people are unvaccinated.
Yellow fever is a viral disease charaterised by flu-like symptoms, but it can lead to complications such as jaundice and renal problems. Approximately 200,000 cases are reported each year, resulting in 30,000 deaths.
It is clear that if the WHO wishes to completely eradicate poliovirus, then it must take lessons from the case of Yellow fever, and not become complacent in administering vaccines.