Authored by: Venkat Rao
Polio, a potentially deadly and disabling infectious diseases caused by poliovirus appears to be making a comeback. Past week, the New York City and State Departments of Health reported detection of polio virus in New York city wastewater samples.
Detection of polio virus, which causes polio, a potentially life-threatening or disabling illness, in wastewater samples indicates likely circulation of the virus in the New York metropolitan area. New York public health officials reacted to the news as “alarming, but not surprising” as they continue active surveillance to assess spread of the virus in the environment. Poliovirus is highly infectious and spread from person to person either through fecal-oral transmission or through oral-oral route. Most infected individuals show no symptoms of the disease, as they spread the infection.
In an earlier report from the Harvard Health Journal, United Kingdom Health Security Agency reported detection of poliovirus in the wastewaters from multiple locations of London, one of the least expected places on earth to detect poliovirus in sewers.
How concerned should all of us be about these reports on the deadly poliovirus?
Multiple public health surveillance reports of vaccine-derived poliovirus in sewage in London and New York are reported from high-income localities with good sanitation and where the oral polio vaccine is not in use, and that the transmission of virus in the surrounding communities is more widespread than the current general estimates. This situation poses potentially serious risk of polio disease among unvaccinated individuals. Since transmission of the viral strains used in the US and UK vaccination have no precedence to vaccine-induced polio disease, the nature and extent of health security risk posed to these communities now under closer surveillance is unclear. The City of Boston is looking to screen wastewater samples for poliovirus in response to reports from London and New York.
Detection of poliovirus in sewage is generally known in communities with the disease outbreak. The more glaring issue is that the reversion of vaccine strains to regain virulence, which generally occurs in communities with low immunization coverage. A greater frequency of vaccine-induced polio outbreak is reported in the past few years with 1113 cases reported from 27 countries in 2020 alone. Note, that the wild poliovirus caused infections is low, which was about 140 cases reported only from Afghanistan and Pakistan, where the vaccination levels are lower compared to the rest of the world.
Hence, the current trend in polio resurgence in high-income communities from the US and UK are the highest number of polio cases in over a decade and may indicate a much higher level of poliovirus circulation in these communities posing a serious challenge to the global polio eradication program. and placing a major public health security challenge to the United States.
According to a research study published past week in Lancet, there is evidence of genetic linkages between the poliovirus detected in London and New York and another study on sewage samples from Jerusalem, Israel. This is despite the fact that Israel is among the countries with highest level of polio vaccination. Reports of vaccine-derived polio presents serious challenge to global polio eradication efforts. Total eradication requires complete disruption of infection from both wild-type polio and vaccine-derived polio strains.
Why is polio reappearing in the US?
Extensive and highly successful polio vaccination in the US has made this country polio-free since 1979, and so is the case with most of the rest of the countries in the world. Now several reports from public health agencies in London, New York, and Jerusalem have repeatedly found poliovirus in wastewater samples with one case of polio reported in New York City. Earlier, in July, New York State Department of Health reported the first case of polio in a Rockland county resident.
The virus was identified as polio Sabin type2 virus, which is indicative of an individual who would have received the oral polio vaccine and may have originated outside the United States. Oral polio vaccine was discontinued in the US due to a higher risk of vaccine-induced polio among those receiving the oral polio vaccine. Since 2000, as a mandatory requirement, children in the US are vaccinated with Inactivated Poliovirus Vaccine (IPV).
The last case of wild polio detected in the US was in 1979. In 1988 World Health Organization adopted the goal for global polio eradication by 2000. The last case of polio reported in the North and South American Continents was in 1991. Western hemisphere was certified as polio-free in 1994, a major accomplishment primarily with the use of the oral polio vaccine. According to CDC, the US remained free of polio only by reducing or eliminating the risk for poliovirus importation through immigration.
World Health Organization provides regular updates on both wild poliovirus and vaccine-induced polio risk categories for all countries. The 2022 WHO update affirms the global risk of polio outbreak due to both wild poliovirus and vaccine-derived poliovirus is a clear and present threat.
CDC Technical Directive, released in June 2022, for polio screening reasserts medical screening for polio as a key step for all categories of immigrants entering the United States. According to the Technical Directive, the polio screening will remain effective until further notice as the current global wild poliovirus transmission creates unacceptable levels of risk of introduction of the virus into the United States. The reported findings of poliovirus in sewage waters in New York and a confirmed case of polio in that city, is an added confirmation of vaccine-derived polio from a source outside of the United States.
How to break virus transmission towards eradication?
Published studies and polio surveillance points out that the Global Polio Eradication 2022-26 Strategy need the following urgent interventions: First, global polio surveillance is essential, particularly in countries with a high disease burden to delineate wildtype polio and vaccine-derived polio cases. Second, despite impressive global efforts towards polio eradication, the current vaccination coverage is still spotty. Note that as long as poliovirus remain in circulation both vaccinated and unvaccinated individuals are at risk of contracting the paralyzing infectious disease. Finally, vaccination intervention must cover both unvaccinated and under vaccinated individuals to address new and unexpected polio outbreaks.
Polio virus in New York and London sewage and reported cases of polio indicates a much wider prevalence of the virus transmission in the Western Hemisphere. With increased global migration and international travel, polio eradication still remains a critical US public health security challenge.