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Infants infected with vaccine-derived polio in Myanmar
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Two children have contracted circulating vaccine-derived poliovirus type 2 with accompanying acute flaccid paralysis in Myanmar, according to WHO.
“The Ministry of Health, supported by WHO and partners of the Global Polio Eradication Initiative, is engaging in implementing an urgent outbreak response plan,” WHO officials wrote in a news release. “The Ministry of Health plans to conduct at least three more large-scale [supplementary immunization activities] in Rakhine and neighboring provinces as well as other identified ‘high risk’ areas of the country, between now and the end of February 2016.”
The children, aged 16 months and 28 months, experienced the onset of paralysis, a common indicator of polio infection, on October 5 and April 16, respectively. Both are from the same township in Rakhine, which borders Bangladesh. The Myanmar Ministry of Health has begun a detailed investigation in the affected area. Officials collected stool samples from 28 households and community contacts of the infected children for laboratory investigation. WHO officials identified three additional acute flaccid paralysis cases, and their cause is under investigation.
WHO officials noted that the genetic diversion between the polio isolates collected in April and October suggest that vaccine-derived polio may have been circulating for more than 1 year.
According to the news release, polio vaccination coverage in Myanmar is approximately 76%, with lower coverage among those with special risks. Worldwide withdrawal of type 2 oral polio vaccine (OPV) is scheduled for April, when bivalent OPV will replace trivalent OPV.
WHO officials recommend that travelers to the area be fully vaccinated against polio before arriving.
“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
Katherine Seib
When the World Health Assembly endorsed the goal to eradicate polio in 1988, there were approximately 350,000 cases of paralysis caused by three wild polioviruses (WPV1, WPV2, or WPV3), and 125 countries were considered endemic for polio. Since then, tremendous progress has been made and 2015 appears to have the lowest incidence of WPV-induced paralytic polio ever with only 66 cases caused by WPV1 reported as of December 15, and only two countries, Pakistan and Afghanistan, with WPV-induced polio cases. Further, WPV2 has been certified as eradicated, the last naturally occurring case had onset in 1999. WPV3 appears on the way to eradication with no cases detected since November 10, 2012 in Nigeria.
But WPVs are not the only causes of polio. The live oral polio vaccine (OPV), the main vaccine used in the eradication program, can rarely cause polio in one of two ways. First, the vaccine virus can mutate and regain neurovirulence causing vaccine-associated paralytic polio (VAPP) in the vaccine recipient or a close contact. Second, the vaccine viruses can be transmitted among susceptible persons, particularly where vaccine coverage is low, regaining both the neurovirulence and transmissibility phenotypes of WPVs. These viruses are known as circulating vaccine-derived polioviruses (cVDPVs) and can lead to outbreaks.
Of the estimated 300 to 500 cases of VAPP annually, 100 to 200 cases are caused by the type 2 virus in the trivalent OPV (tOPV). Since 2000, there have been about 800 cVDPVs reported. Type 2 cVDPV has accounted for nearly 90% of all cVDPVs. Thus, in the absence of WPV2 circulation, several thousand persons may have been paralyzed by type 2 vaccine viruses in the 16 years since WPV2 has disappeared. Therefore, to truly eradicate polio of all causes, not only must the WPVs be eradicated, but VAPP and cVDPVs must be stopped by discontinuing use of OPV.
As a first step, withdrawal of the type 2 component from tOPV is planned for the last 2 weeks of April with a switch to bivalent, types 1 and 3 OPV (bOPV), an unprecedented, global and synchronized effort. To induce some level of type 2 immunity in the population born after the switch, at least one dose of trivalent inactivated polio vaccine (IPV) is now being recommended in the routine schedule — another extraordinary global effort. Other efforts to maximize type 2 immunity prior to the switch include tOPV mass campaigns and stockpiling monovalent type 2 OPV (mOPV2) for potential outbreak control, if needed, and containment or destruction of laboratory specimens containing type 2 viruses, among other measures.
A threat to maintaining type 2 polio-free status are potential outbreaks of cVDPV2s. That’s why the Myanmar situation is so important and extensive efforts are underway to terminate cVDPV2 transmission in the country so that it does not become a reservoir to reinfect other countries with type 2 virus after the global switch. Other persistent chains of type 2 cVDPVs have been terminated, and the steps being taken in Myanmar should lead to stopping that outbreak and helping to pave the way for a polio-free world.
U.S. physicians should be alert to polio in the differential diagnosis of a child who presents with acute flaccid paralysis, reporting suspected cases immediately to the health department, obtaining at least two stool specimens at least 24 hours apart within 14 days of onset of paralysis and sending them to an accredited laboratory for analysis. Health departments can assist with this. Also physicians can advocate that resources are assured to the Global Polio Eradication Initiative (GPEI) to assure the job of eradication is finished and we achieve and sustain a polio-free world.
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
Katherine Seib, MSPH
Division of Infectious Diseases
Emory University School of Medicine
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