India’s recent polio scare has highlighted that maintaining vigilance against the disease is of the utmost importance — even four years after its eradication in the country was declared.
The Union Health Ministry confirmed the contamination of a number of batches of vaccines with type-2 poliovirus vaccine in three states: Maharashtra, Telangana and Uttar Pradesh. The last type-2 wild poliovirus case was detected in 1999. The last polio case due to wild poliovirus in the country was detected on January 13, 2011.
This is of particular concern due to the fact that type-2 vaccine is no longer in use. In September 2015, the World Health Organization (WHO) declared type-2 polio fully eradicated. On the WHO’s advice, India phased out the type-2 virus from its oral vaccines in April 2016.
Endgame strategies for polio eradication
The reason the type 2 strain was phased out from vaccine circulation is due to the potential for vaccine-derived polio. This occurs infrequently in those who receive the vaccination and presents symptoms akin to wild type polio. Issues arise when immunisation levels are low within a community. If this is the case the vaccine derived polio strain can circulate among those who have not been vaccinated, stressing the need for high levels of immunisation coverage.
“The vaccine virus is a problem because of all the oral vaccine strains, the strain of type-2 is most likely to cause vaccine-associated paralytic polio, which is why it was removed in the first place,” said public health researcher Sylvia Karpagam.
Fears of a possible resurgence were amplified by the recent discovery of the type-2 strain by government health inspectors in the stool samples of children in Uttar Pradesh. These samples were linked to the contaminated batches of vaccines, which have since been withdrawn and the manager arrested.
India continues to use live, oral polio vaccines which contain types 1 and 2. Many countries use the more expensive inactivated polio vaccine (IPV) — containing a dead virus which presents no opportunity for vaccine derived infections.
The current WHO “Endgame Plan” calls for the introduction of at least one dose of IPV into routine immunization schedules along with the withdrawal of OPV in a phased manner to reduce vaccine derived infections. This process began with the removal of the type-2 strain from vaccination schedules following global eradication.
The situation of India’s healthcare system has made the eradication of other diseases all but impossible
Diseases such as leprosy indicate the progress India has made in combatting some infectious diseases. Leprosy was officially eliminated as of 2005. Elimination of a disease is, however, different from eradication. Elimination is described as a prevalence rate of less than one case per 10,000 population at the national level, while eradication is where there are no new cases of the disease occurring within the country.
India currently holds 57 percent of the world’s leprosy patients, with Brazil and Indonesia also having high numbers of leprosy cases. Despite the disease being eliminated in India the rate of 0.68 per 10,000 cases is still higher than the global average of 0.2 per 10,000.
One of the key issues with the declaration of elimination is that elimination is often conflated with eradication. Without knowledge of the difference between the two, many may believe that the disease is gone for good. The announcement of elimination can even influence funding to fight the disease. As the disease is no longer seen as the threat to public health it once was, funding from government and non-government bodies alike may fall.
India shares an issue with many developing nations — unequal access to healthcare. Due to the vast differences in geographies and wealth gaps in India, access to medical treatment differs considerably. Many rural environments will struggle to obtain even basic medical treatment.
Due to the disparities in healthcare access rural locations can often act as reservoirs for diseases. Despite the announcement of elimination in 2005, the rates of leprosy in many areas now exceed the levels that qualify for the classification of elimination. The proportion of districts with prevalence exceeding one in 10,000 population has increased to 18.8 percent, up from 15.3 percent in 2012.
Lessons learned from polio
The Polio Eradication Campaign in India has seen widespread praise as an example of a well thought out, and well implemented healthcare campaign. Vigilance must be maintained to ensure India remains polio free, this is especially true due to India’s proximity to the countries harbouring the world’s last remaining wild type cases.
One of the reasons for the success of the polio campaign is the ability to vaccinate against it. Vaccination campaigns can show high levels of effectiveness even in areas with little healthcare infrastructure if large scale vaccination campaigns are arranged.
Political will must be maintained in the case of eradication of vaccine preventable diseases to ensure that immunisation levels remain high in the years following eradication to ensure that resurgence is not a possibility.
Diseases that are not vaccine preventable are far more difficult to control in areas with limited healthcare infrastructure. If the healthcare system is not equipped to deal with the disease then there is little that can be done without extensive campaigns targeting the disease.
In the case of leprosy the instance of disease has once again begun to creep up since its announcement of elimination. The rapid response to the recent polio scare shows a level of political commitment to ensuring the disease stays eradicated, this could serve as a lesson to other diseases that are approaching eradication levels. Reducing vigilance when the end goal of eradication is in sight could see all progress lost.