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Children infected with vaccine-derived polio in Ukraine
Two children have contracted circulating vaccine-derived poliovirus type 1 with accompanying paralysis in southwestern Ukraine, according to WHO.
“Discussions are currently ongoing with national health authorities to plan and implement an urgent outbreak response,” WHO officials wrote in a news release. “An outbreak response of internationally agreed standard, as adopted by the World Health Assembly in May 2015, requires a minimum of three large-scale supplementary immunization activities with an appropriate oral polio vaccine, to begin within 2 weeks of confirmation of the outbreak and covering a target population of 2 million children aged less than 5 years, and the public declaration of the outbreak as a national public health emergency.”
The children, aged 4 years and aged 10 months, experienced the onset of paralysis, a common indicator of polio infection, on June 30 and July 7, respectively. Both are from the Zakarpatskaya region of Ukraine, located on the border of Romania, Hungary, Slovakia and Poland.
According to WHO, Ukraine was at a significant risk for a vaccine-derived polio outbreak because only half of its children were vaccinated for polio and other vaccine-preventable diseases as of 2014.
WHO officials recommend that all residents within the region receive additional doses of oral polio vaccine or inactivated polio vaccine. Travelers to the area are advised to be fully vaccinated against polio before arriving.
Due to surveillance deficits and coverage gaps in the population, WHO is committed to a “robust outbreak response.” The risk for an outbreak is considered “high” because of the infected region’s proximity to other countries.
“It is important that all countries, in particular those with frequent travel and contacts with polio-affected countries and areas, strengthen surveillance for cases of acute flaccid paralysis in order to rapidly detect any new virus importation and to facilitate a rapid response,” WHO officials wrote.
Perspective
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Walter A. Orenstein
Julie R. Garon
However, oral polio vaccine (OPV) can cause polio, either as vaccine-associated paralytic polio which occurs in vaccine recipients or their close contacts, or as circulating vaccine-derived polioviruses (cVDPVs). These cVDPVs result from transmission of vaccine viruses from susceptible person to susceptible person, allowing mutations to occur. The viruses regain both the neurovirulence and transmissibility properties of the wild poliovirus (WPV) phenotype.
These cVDPVs can lead to outbreaks of polio, albeit rarely. From 2001 to 2011, cVDPVs caused only about 500 cases of paralysis while the use of OPV during that period prevented more than 3.5 million cases of paralysis due to WPV. The most important risk factor for emergence and spread of cVDPVs is immunity gaps resulting from low immunization coverage; Ukraine is a country where only half of the children are fully immunized against polio.
With so few WPV cases seen globally at this stage in the eradication effort, cVDPV outbreaks in places like Ukraine, where paralytic polio has not been experienced in years, are cause for concern. To terminate transmission of cVDPVs, WHO recommends at least three mass vaccination campaigns with an appropriate oral polio vaccine to begin within 2 weeks of detection of the outbreak, covering a target population of at least 2 million children aged less than 5 years. Ukraine is now embarking on such an effort to stop transmission of its cVDPV type 1 virus.
There are several lessons coming out of this outbreak. First, there is a need to maintain high immunization coverage in the routine immunization program against polio, which did not occur in Ukraine. Second, it is important that physicians suspect polio in persons who present with a clinically-compatible syndrome of acute flaccid paralysis; this means collecting at least two stool specimens no less than 24 hours apart within 14 days of onset of paralysis and assuring the specimens are transported to a laboratory capable of detecting polio. In the US, physicians should immediately contact their local or state health department for help. As most polio infections are asymptomatic, a case may be the result of transmission within the US and there may be no travel history to polio-infected areas.
Third, to truly eradicate all polio, the use of OPV must be stopped globally. Plans are underway to stop OPV in a phased fashion, beginning with elimination of the type 2 component since there has been no naturally-occurring type 2 polio since 1999; only types 1 and 3 WPVs have caused outbreaks in recent years. Fourth, physicians should assure patients traveling to polio infected areas are vaccinated including one time boosters with inactivated polio vaccine, for those who were previously fully immunized.
Walter A. Orenstein, MD
Infectious Diseases in Children Editorial Board member
Emory University School of Medicine
Julie R. Garon, MPH
Division of Infectious Diseases
Emory University School of Medicine