Emergencies preparedness, response

Circulating vaccine-derived poliovirus type 1 – Myanmar

Disease outbreak news
22 August 2019

On 23 June 2019, a vaccine-derived poliovirus type 1 (VDPV1) was isolated from a two -year- old child with acute flaccid paralysis (AFP), with onset of paralysis on 22 May 2019 from Kayin state, Myanmar. Subsequently, on 11 July 2019, a genetically linked VDPV1 was isolated from the same state from a 5-year 6-month-old child with AFP, with date of onset of paralysis on 14 June, and it was classified as circulating VDPV1 (cVDPV1) on 12 July 2019. On 25 July 2019, cVDPV1 was isolated from a third AFP case from the same state, with date of onset of paralysis on 23 May 2019. Subsequently, on 19 August 2019, a fourth case of VDPV1 has been confirmed in a six-year-old child, with onset of paralysis on 23 July 2019. The child has no history of vaccination with OPV. In addition, the virus has also been isolated from seven healthy community contacts. These linked viruses have 25 to 31 nucleotide changes from Sabin 1. All cases and contacts are from Hpapun township of Kayin state, Myanmar.

Myanmar’s routine immunization coverage is estimated at 91% for three doses of bivalent oral polio vaccine (bOPV) in 2018. Neighbouring countries including Thailand and other countries in South East Asia have been informed of the confirmed cVDPV1, and subnational surveillance is being strengthened across the region. In 2018, Myanmar and Kayin state met certification standards for AFP surveillance with non-polio AFP rate of 3.45, and stool adequacy rate of 100% for Kayin state.

In Myanmar, the last cVDPV1 outbreak was reported in 2007 with 4 cases. Also, in 2015, cVDPV2 outbreak was reported in Rakhine state with 2 confirmed cases.

Public Health Response

  • The Ministry of Health (MOH) and local health authorities are undertaking strong measures to stop the transmission of cVDPV1 and the partners of the Global Polio Eradication Initiative (GPEI) are providing support as required;
  • A full epidemiological and virological field investigation has been conducted, including a thorough risk assessment;
  • Active surveillance is being strengthened and subnational population immunity levels have been analyzed;
  • Three vaccination campaigns with bOPV have been conducted in 12 townships targeting about 300,000 children under the age of five years;
  • Two large scale bOPV vaccination campaigns are being planned for August and October 2019 to cover 98 high risk townships across the country, targeting 1.2 million children under the age of five years;
  • Other regions/states have been alerted to improve immunization and AFP surveillance.

WHO risk assessment:

The detection of cVDPVs underscores the importance of maintaining high routine vaccination coverage everywhere to minimize the risk and consequences of any poliovirus circulation as well as the need to ensure quality surveillance for early detection of any polioviruses. These events also underscore the risk posed by any low-level transmission of the virus. A robust outbreak response is needed to rapidly stop circulation and ensure sufficient vaccination coverage in the affected areas to prevent similar outbreaks in the future.

For this event, the overall public health risk at national level is considered to be high due to:

  • Low socio- economic conditions and limited public health infrastructure in some parts of Kayin state
  • Accumulated susceptible population due to low population immunity among specific Kayin state population, which poses a risk of ongoing transmission within and across the state.
  • Hard-to-reach area with accessibility challenges due to security concerns, and geographical location which hamper the vaccination and the implementation of response actions.
  • The low routine immunization coverage in the affected areas provides favourable conditions for the expansion of a possible polio virus outbreak across different areas in the country.
  • The high number of nucleotide changes of the cVDPV1 isolates, the recent discovery of new cases and the evidence of healthy contacts being infected indicates that the virus may have been circulating for a long time, thus increasing the risk of spread.
  • Although Kayin state met certification standard of AFP surveillance (2017-2018), there might be pockets of ongoing transmission which are not timely detected.
  • The limited accessibility for health care providers in certain areas in Kayin state including the affected Hpapun township, which impedes the implementation of response measures.

As per UNHCR, as of June 2019, 95,681 refugees from Myanmar, most of them belonging to ethnic minorities from Kayin state, are living in nine refugee camps in Thailand. The polio immunization coverage of Thailand is high, and a joint field visit conducted by WHO Country Office and MOH-Thailand following notification of cVDPV in Myanmar confirms that the coverage of OPV is 93.3% in these camps in 2018.

WHO will continue to evaluate the epidemiological situation and outbreak response measures being implemented.

WHO advice

It is important that all countries, in particular those with frequent travel and contacts with polio- affected countries and areas, strengthen polio surveillance in order to rapidly detect any new virus importation and to facilitate a rapid response. Countries, territories and areas should also maintain uniformly high routine immunization coverage at the district level to minimize the consequences of any new virus introduction.

WHO’s International Travel and Health recommends that all travellers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than 4 weeks) from infected areas should receive an additional dose of OPV or inactivated polio vaccine (IPV) within 4 weeks to 12 months of travel.

As per the advice of an Emergency Committee convened under the International Health Regulations (2005), efforts to limit the international spread of poliovirus remains a Public Health Emergency of International Concern (PHEIC). Countries affected by poliovirus transmission are subject to Temporary Recommendations. To comply with the Temporary Recommendations issued under the PHEIC, any country infected by poliovirus should declare the outbreak as a national public health emergency and consider vaccination of all international travellers.

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