Statement of the Twentieth International Health Regulations (IHR) Emergency Committee regarding the International Spread of Poliovirus

Wild Poliovirus

Worldwide there are three remaining endemic countries, with Afghanistan and Pakistan being the only two countries where wild poliovirus (WPV) transmission is continuing to be reported. The committee noted that it is more than four years since there has been international spread outside of these two epidemiologically linked countries.

However, the Committee was very concerned by the increase in WPV1 cases globally in 2018, with more cases in the two countries than in 2017.  This trend appears to be continuing in 2019, with six cases already compared to two for the same period in 2018.  Furthermore, international spread between the two countries has continued, after an earlier 10-month period of no international spread between the two neighbors.

Vaccine derived poliovirus

There are now eight countries in four WHO Regions responding to outbreaks of circulating Vaccine Derived Poliovirus (cVDPV), an unprecedented number of outbreaks in recent years.  The new outbreak of cVDPV1 in Indonesia exemplifies the gaps in population immunity in many parts of the world considered polio free.  It appears likely that there has been missed transmission of this virus for several years although there is no evidence so far that this has occurred outside of Papua province.

The new outbreak of cVDPV2 in Mozambique is a serious concern, as it may be linked to inadequate controls placed upon unused vials  of monovalent Oral Polio Vaccine Type 2 (mOPV2) during the earlier event there in 2017.  The committee noted that the case occurred close to the border with Malawi, prompting concern about the opportunity for international spread.

The cVDPV2 outbreaks in Nigeria highlight the vulnerability to poliovirus infection in many parts of the country, with the virus spreading to areas not previously considered at high risk of polio, such as Kwara.  Although no international spread of WPV1 has been observed from Nigeria since 2014, the recent cases of importation of cVDPV2 into Niger is concerning, given that cVDPVs have rarely spread across borders in the past.  The committee was concerned by the lack of progress in controlling this outbreak, and the proximity of a recent case to the Republic of Benin.

The outbreak of cVDPV2 in Somalia and Kenya is another infrequent example of international spread of cVDPV across borders.

Countries neighboring Somalia, such as South Sudan, Ethiopia and Djibouti, have areas of weak surveillance which poses a risk that international spread may go undetected.

Although there are indications that transmission may be slowing in DR Congo, the protracted duration of the outbreak, ongoing conflict, insecurity and population movements within and outside the country represent a significant risk of spread.

The committee noted that in all infected countries, routine immunization was weak, and coverage remains very poor in many areas of these countries.

Inaccessibility is a major risk to interruption of transmission in Nigeria, Niger, Somalia and Afghanistan.

Conclusion

The Committee unanimously agreed that the risk of international spread of poliovirus remains a Public Health Emergency of International Concern (PHEIC) and recommended the extension of Temporary Recommendations for a further three months starting 28 February 2019.

Temporary Recommendations are applicable to countries in the following Risk Categories:

States infected with WPV1, cVDPV1 or cVDPV3 with potential risk of international spread

WPV1                                                                     

• Afghanistan                         (most recent detection 26 January 2019)
• Pakistan                                        (most recent detection 28 January 2019)
• Nigeria                                (most recent detection 27 Sept 2016)

cVDPV1

• Papua New Guinea                        (most recent detection 7 November 2018)
• Indonesia                                           (most recent detection 25 January 2019)

cVDPV3

• Somalia                                               (most recent detection 7 Sept 2018)

• DR Congo         (most recent detection 7 October 2018)
• Kenya                (most recent detection 21 March 2018)
• Mozambique  (most recent detection 17 December 2018)
• Niger                  (most recent detection 5 December 2018)
• Nigeria                              (most recent detection 15 January 2019)
• Somalia                             (most recent detection 11 October 2018)

States no longer infected by WPV1 or cVDPV, but which remain vulnerable to re-infection by WPV or cVDPV

WPV1

• Cameroon                                                   (last case 9 Jul 2014)
• Central African Republic                        (last case 8 Dec 2011)
• Chad                                                              (last case 14 Jun 2012)

CVDPV

• Syria                                                              (last case 21 Sept 2017)

Useful Links:

Link to the Statement of the Twentieth IHR Emergency Committee:

https://www.who.int/news-room/detail/01-03-2019-statement-of-the-twentieth-ihr-emergency-committee

Link to the updated WHO fact sheet on Poliomyelitis (1 March 2019):

https://www.who.int/news-room/fact-sheets/detail/poliomyelitis