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The thirty-seventh meeting of the Emergency Committee under the International Health Regulations (2005) (IHR) on the international spread of poliovirus was convened by the WHO Director-General on 12 December 2023 with Committee members and advisers meeting face to face, and via video conference with affected countries, supported by the WHO Secretariat. The Emergency Committee reviewed the data on wild poliovirus (WPV1) and circulating vaccine derived polioviruses (cVDPV) in the context of the global target of eradication of WPV and cessation of outbreaks of cVDPV2. Technical updates were received about the situation in the following countries: Afghanistan, Egypt, Guinea, Mauritania, Nigeria, Pakistan and Zimbabwe.

Wild poliovirus

There have been four new cases of WPV1 in Pakistan since the last meeting, bringing the total to six in 2023. Furthermore, there has been a large increase in environmental detections, with 60 positive samples found in the three months from September to November, bringing the total in 2023 to 82. After a period of non-detection, new transmission is occurring in the Quetta Block in Balochistan, in Karachi in Sindh, Islamabad / Rawalpindi and in Peshawar in Khyber Pakhtunkhwa (KP) province. Although implementation of a polio action plan in southern KP has resulted in 160,000 more children being vaccinated, the context remains challenging: political instability, insecurity in some areas, with front line workers requiring police patrols to accompany them, and vaccination boycotts where communities make demands for other services in exchange for allowing polio vaccination. The programme continues to miss a significant number of children in Pakistan.

Since the last meeting, there have been no new WPV1 cases reported from Afghanistan, where the total number of cases remains six, all from Nangarhar province. However, there have been 46 WPV1 positive environmental samples to date in 2023, mostly from the endemic East Region (Nangarhar and Kunar provinces), but recently also in environmental samples from Kabul, Kandahar, Zabul and Balkh provinces.

This indicates spread of WPV1 from the endemic zones of Afghanistan (East Region) and Pakistan (South KP) and is a reversal of recent progress. The programme is implementing high quality campaigns and reaching more children than ever before, but the quality will have to be increased further and sustained. Any setback in Afghanistan poses a risk to the programme in Pakistan due to high population movement.

Afghanistan continues to implement an intense campaign schedule, focusing on improving quality in the endemic zone and timely response to WPV1 detections elsewhere in the country. Quality improvement interventions in the East Region include microplan validation, enhancing engagement of female vaccinators, social mobilizers and monitors, intensified and well-supervised trainings of the polio health workers, intensified monitoring, using polio campaign microplans to accelerate routine immunization and expanding the campaign-target age group up to 10 years in the areas that were inaccessible prior to 2021. While the campaign-quality in the East Region has improved in 2023, there are continued challenges in the South Region where almost 200,000 children remain unreached during the campaigns and quality is sub-optimal as indicated by the lot quality assurance sampling (LQAS).

The recent major increase in the number of Afghan returnees from Pakistan has compounded the humanitarian challenges in Afghanistan. The country received close to 0.3 million Afghan returnees from mid-September to mid-November and the expected total number of returnees is 1.7 million. This massive population movement significantly increases the risk of cross-border poliovirus spread as well as spread within the two countries. The polio programme in Afghanistan has activated a contingency plan and deployed additional teams and supervisors in critical areas and routes to vaccinate the children in the returnee populations. Close coordination is being maintained with UNHCR and IOM for vaccination at their centres and for information sharing. Districts with significant influx of returnees will be included in the upcoming polio vaccination campaigns.

It has now been more than 15 months since the WPV1 detection in south-eastern Africa, with the last case having onset of paralysis on 10 August 2022 in Mozambique, and it has been two years since the single case was detected in Malawi. The Committee noted that the GPEI carried out independent outbreak response assessments (OBRA’s) in Mozambique and Malawi in November 2023. In Mozambique, there are promising signs that the transmission of imported WPV1 in Mozambique has stopped. However, a full 12 months of finalized surveillance data was not yet available. In Malawi, the OBRA team concluded that the WPV1 transmission in Malawi has most likely stopped. However, the WPV1 outbreak will only be considered as closed once a similar conclusion is reached for Mozambique. Formal closure of the outbreak will be by the WHO Regional office following endorsement of the Regional Certification Commission.

Circulating vaccine derived poliovirus (cVDPV)

The number of cVDPV2 cases is declining and the geographic concentration is more focused, with a modest reduction in the number of infected provinces and districts. In 2023 to date, there have been 374 cases confirmed with cVDPV, of which 265 are cVDPV2 and 109 are cVDPV1. Of these 374 cases, 191 (51%) have occurred in the DR Congo. Globally 72% of cases are in the four most consequential geographies (eastern DR Congo, northern Nigeria, northern Yemen and Somalia). There are also decreasing numbers of new and circulating emergence groups. Despite the ongoing decline in the number of cVDPV2 cases and the number of lineages circulating, the risk of international spread of cVDPV2 remains high. Evidence of this includes the high transmission in DR Congo with recent spread of cVDPV2 to Tanzania, and new emergences in Zimbabwe and Egypt, and re-infection of Guinea and Mauritania. Zimbabwe itself has never used the vaccine, so the detection indicates an importation of PV2 from an unknown source.

The Committee noted that in the African Region, which now uses novel OPV2 exclusively, there have been a total of 10 new cVDPV2 emergences detected that have emerged from novel OPV2 use, while there has been one such emergence identified in Egypt in the Eastern Mediterranean Region. The detection of nOPV2-derived VDPV2 strains is an expected finding with increased nOPV2 use. The vaccine nOPV2 continues to demonstrate significantly higher genetic stability and substantially lower likelihood of reversion to neurovirulence relative to Sabin OPV2. Since first use in March 2021, approximately 821 million doses of nOPV2 have been administered in the African Region. It is estimated that the 10 emergences from AFR represent an 82% lower risk of emergence by nOPV2 than Sabin OPV2 in the African Region.

Overall, there has been a trend toward fewer but bigger campaigns. An OPV supply disruption contributed to reduction in campaign activity in the first quarter of 2023 but supply is now sufficient. Timeliness of response is a challenge; over the past 18 months, only 29% of campaigns met the target of implementing the first campaign within 28 days of outbreak confirmation.

The emergence and ongoing transmission of cVDPV1 in Madagascar, DR Congo and Mozambique is of concern as it highlights gaps in population immunity to type 1 polioviruses including WPV1 in the sub-region. Of the 426 children reported in 2023 with paralysis due to cVDPV, over a quarter are confirmed due to type 1. Furthermore, this gap in population immunity poses a major risk for WPV1 importation and further spread, putting the global eradication target at risk.

The Committee noted that much of the risk for cVDPV outbreaks can be linked to a combination of inaccessibility, insecurity, a high concentration of zero dose children and population displacement. These factors are most evident in northern Yemen, northern Nigeria, south central Somalia and eastern Democratic Republic of the Congo, but also in northern Mozambique, Burkino Faso and Mali. The instability in West Africa and the Sahel region, most recently in Niger was especially concerning, as the risk of polio program disruption was particularly high.

Conclusion

The Committee unanimously agreed that the risk of international spread of poliovirus still remains a Public Health Emergency of International Concern (PHEIC) and recommended its extension and that of the Temporary Recommendations for a further three months. The Committee considered the following factors in reaching this conclusion:

Ongoing risk of WPV1 international spread:

Based on the following factors, the risk of international spread of WPV1 remains:

• re-infection of epidemiologically critical areas and historical reservoirs like Karachi and the Quetta Block in Pakistan and Kandahar in Afghanistan represents a significant risk to the gains made during the last 18 months;
• the actual spread of WPV1 lineages seen predominantly in Afghanistan in 2022 now being detected in Pakistan in 2023;
• high-risk mobile populations in Pakistan represent a specific risk of international spread to Afghanistan in particular, compounded by the large number of returnees from Pakistan into various parts of Afghanistan;
• the large pool of unvaccinated ‘zero dose’ children in southern Afghanistan constitutes a major risk;
• some areas of Afghanistan still only allow site to site or mosque to mosque immunization response, which has been shown to be less effective than the house to house modality;
• although it is likely transmission of WPV1 has been interrupted in Malawi and Mozambique, the route from Pakistan to Africa remains unknown;
• pockets of insecurity in the remaining endemic transmission zones.

Ongoing risk of cVDPV international spread:

Based on the following factors, the risk of international spread of cVDPV2 appears to remain high:

• the outbreak of cVDPV1 in and ongoing high transmission of cVDPV2 in eastern Democratic Republic of the Congo and cVDPV2 in north-western Nigeria, which have caused international spread to neighboring countries;
• ongoing cross border spread including into newly infected countries such as Zimbabwe, and re-infection of Egypt due to local emergence and Mauritania and Guinea by importation;
• the long distance spread by air travel of cVDPV2 between Israel, the United Kingdom and the USA;
• the ever-widening gap in population intestinal mucosal immunity in young children since the withdrawal of OPV2 in 2016 and consequently high concentration of zero dose children in certain areas;
• insecurity in those areas that are the source of cVDPV transmission.

Contributing factors include:

• Weak routine immunization: Many countries have weak immunization systems that can be further impacted by humanitarian emergencies including conflict and protracted complex emergencies. This poses a growing risk, leaving populations in these fragile states vulnerable to polio outbreaks.
• Lack of access: Inaccessibility continues to be a major risk, particularly in northern Yemen and Somalia which have sizable populations that have been unreached with polio vaccine for extended periods of more than a year.

Risk categories

The Committee provided the Director-General with the following advice aimed at reducing the risk of international spread of WPV1 and cVDPVs, based on the risk stratification as follows:

1. States infected with WPV1, cVDPV1 or cVDPV3.
2. States infected with cVDPV2, with or without evidence of local transmission.
3. States previously infected by WPV1 or cVDPV within the last 24 months.

Criteria to assess States as no longer infected by WPV1 or cVDPV:

• Poliovirus Case: 12 months after the onset date of the most recent case PLUS one month to account for case detection, investigation, laboratory testing and reporting period OR when all reported AFP cases with onset within 12 months of last case have been tested for polio and excluded for WPV1 or cVDPV, and environmental or other samples collected within 12 months of the last case have also tested negative, whichever is the longer.
• Environmental or other isolation of WPV1 or cVDPV (no poliovirus case): 12 months after collection of the most recent positive environmental or other sample (such as from a healthy child) PLUS one month to account for the laboratory testing and reporting period.
• These criteria may be varied for the endemic countries, where more rigorous assessment is needed in reference to surveillance gaps.

Once a country meets these criteria as no longer infected, the country will be remain on a ‘watch list’ for a further 12 months for a period of heightened monitoring. After this period, the country will no longer be subject to Temporary Recommendations.

TEMPORARY RECOMMENDATIONS

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

These countries should:

• Officially declare, if not already done, at the level of head of state or government, that the interruption of poliovirus transmission is a national public health emergency and implement all required measures to support polio eradication; where such declaration has already been made, this emergency status should be maintained as long as the response is required.
• Ensure that all residents and long­term visitors (> four weeks) of all ages, receive a dose of bivalent oral poliovirus vaccine (bOPV) or inactivated poliovirus vaccine (IPV) between four weeks and 12 months prior to international travel.
• Ensure that those undertaking urgent travel (within four weeks), who have not received a dose of bOPV or IPV in the previous four weeks to 12 months, receive a dose of polio vaccine at least by the time of departure as this will still provide benefit, particularly for frequent travelers.
• Ensure that such travelers are provided with an International Certificate of Vaccination or Prophylaxis in the form specified in Annex 6 of the IHR to record their polio vaccination and serve as proof of vaccination.
• Restrict at the point of departure the international travel of any resident lacking documentation of appropriate polio vaccination. These recommendations apply to international travelers from all points of departure, irrespective of the means of conveyance (road, air and / or sea).
• Further intensify cross­border efforts by significantly improving coordination at the national, regional and local levels to substantially increase vaccination coverage of travelers crossing the border and of high risk cross­border populations. Improved coordination of cross­border efforts should include closer supervision and monitoring of the quality of vaccination at border transit points, as well as tracking of the proportion of travelers that are identified as unvaccinated after they have crossed the border.
• Further intensify efforts to increase routine immunization coverage, including sharing coverage data, as high routine immunization coverage is an essential element of the polio eradication strategy, particularly as the world moves closer to eradication. Countries which have not yet introduced IPV2 into their schedules should urgently implement this. Once available, countries should also consider introducing the hexavalent vaccine now approved by Gavi.
• Maintain these measures until the following criteria have been met: (i) at least six months have passed without new infections and (ii) there is documentation of full application of high quality eradication activities in all infected and high risk areas; in the absence of such documentation these measures should be maintained until the state meets the above assessment criteria for being no longer infected.
• Provide to the Director-General a regular report on the implementation of the Temporary Recommendations on international travel.

States infected with cVDPV2, with or without evidence of local transmission:

States that have had an importation of cVDPV2 but without evidence of local transmission should:

Officially declare, if not already done, at the level of head of state or government, that the prevention or interruption of poliovirus transmission is a national public health emergency

• Undertake urgent and intensive investigations to determine if there has been local transmission of the imported cVDPV2
• Noting the existence of a separate mechanism for responding to type 2 poliovirus infections, consider requesting vaccines from the global novel OPV2 stockpile.
• Further intensify efforts to increase routine immunization coverage, including sharing coverage data, as high routine immunization coverage is an essential element of the polio eradication strategy, particularly as the world moves closer to eradication. Countries which have not yet introduced IPV2 into their schedules should urgently implement this. Once available, countries should also consider introducing the hexavalent vaccine now approved by Gavi
• Intensify national and international surveillance regional cooperation and cross­border coordination to enhance surveillance for prompt detection of poliovirus.

States with local transmission of cVDPV2, with risk of international spread should in addition to the above measures should:

• Encourage residents and long­term visitors to receive a dose of IPV four weeks to 12 months prior to international travel.
• Ensure that travelers who receive such vaccination have access to an appropriate document to record their polio vaccination status.
• Intensify regional cooperation and cross­border coordination to enhance surveillance for prompt detection of poliovirus, and vaccinate refugees, travelers and cross­border populations.

For both sub-categories:

• Maintain these measures until the following criteria have been met: (i) at least six months have passed without the detection of circulation of VDPV2 in the country from any source, and (ii) there is documentation of full application of high quality eradication activities in all infected and high risk areas; in the absence of such documentation these measures should be maintained until the state meets the criteria of a ‘state no longer infected’.
• At the end of 12 months without evidence of transmission, provide a report to the Director-General on measures taken to implement the Temporary Recommendations.

States previously infected by WPV1 or cVDPV within the last 24 months

WPV1

none

cVDPV

These countries should:

• Urgently strengthen routine immunization to boost population immunity.
• Enhance surveillance quality, including considering introducing or expanding supplementary methods such as environmental surveillance, to reduce the risk of undetected WPV1 and cVDPV transmission, particularly among high-risk mobile and vulnerable populations.
• Intensify efforts to ensure vaccination of mobile and cross­border populations, Internally Displaced Persons, refugees and other vulnerable groups.
• Enhance regional cooperation and cross border coordination to ensure prompt detection of WPV1 and cVDPV, and vaccination of high-risk population groups.
• Maintain these measures with documentation of full application of high-quality surveillance and vaccination activities.

Additional considerations

The Committee recognizes the concerns regarding the lengthy duration of the polio PHEIC and the importance of exploring alternative measures, including convening a polio IHR Review Committee to advise the WHO Director-General on the possible issuance of standing recommendations. The Committee noted the current review of the International Health Regulations taking place and that amendments to the Regulations were possible in 2024. The Committee felt it was still too early to discontinue the PHEIC as the risk of exportation of both WPV and cVDPVs remains significant and the removal of the PHEIC may send the wrong message at this critical juncture in polio eradication.

The Committee appreciates the commitment of the Afghan authorities to the global goal of polio eradication, and strongly encourages house to house campaigns be implemented wherever feasible as these campaigns enhance identification and coverage of zero dose and under-immunized children. The Committee noted and strongly supported the ongoing use of female vaccinators, enhancing access to households, with female participation as front line health workers increasing. The large number of returnees from Pakistan represents a significant risk of poliovirus spread, and the country programme needs to put in place risk mitigation measures and ensure vaccination of returning populations to the best possible extent. The committee urges a high-quality vaccination response take place immediately in the Southern Region of Afghanistan, to mitigate the risk of a large polio outbreak.

The Committee noted with concern the new transmission of WPV1 in Pakistan in areas such as Karachi and the Quetta Block, and calls for an aggressive outbreak response in the coming low transmission season, with a response synchronized between the two endemic countries to the maximum extent possible. The Committee commended the national and provincial governments for demonstrating effective programme ownership in Pakistan. This must continue in the upcoming time of planned general elections, and maintenance of the effective roles of provincial chief secretaries, district commissioners and deputy commissioners is critical.

The Committee noted that Egypt is responding effectively to the cVDPV2 outbreak in North Sinai and urges Egypt to ensure this is maintained despite the effect of the war in Gaza which could put pressure on public health resources.

The Committee is concerned about the timeliness of detection of cVDPV2 in Mauritania, and urges Mauritania, Guinea and Mali to coordinate and synchronize activities. Zimbabwe should consider implementing environmental surveillance outside of the capital city Harare if feasible.

Nigeria remains central to stopping outbreaks in the African Region, as cVDPV2 from Nigeria has spread to many other African countries. Within Nigeria, programme quality issues have persisted since 2021, especially in the north-western part of the country. Stopping cVDPV outbreaks in Nigeria will be critical to success in the African Region and globally. The Committee is encouraged by the commitment of the new health leadership in the country and noted that political leadership at all levels in Nigeria must be aligned to address the chronic issues and improve the programme response quality. Lessons learnt from the Borno experience should be applied in the north-western states.

The Committee urged the polio program to strengthen all aspects of surveillance, noting that significant gaps remain in many affected countries, and to continue to address delays in specimens being transported for testing for polioviruses, leading to problems with specimen quality. Noting the challenges of polio surveillance particularly the timeliness of detection, the Committee recommends that the programme continues to strengthen and improve timeliness including by introducing direct detection methods.

Based on the current situation regarding WPV1 and cVDPVs, and the reports provided by affected countries, the Director-General accepted the Committee’s assessment and on 21 December 2023 determined that the poliovirus situation continues to constitute a PHEIC with respect to WPV1 and cVDPV. The Director-General endorsed the Committee’s recommendations for countries meeting the definition for ‘States infected with WPV1, cVDPV1 or cVDPV3 with potential risk for international spread’, ‘States infected with cVDPV2 with potential risk for international spread’ and for ‘States previously infected by WPV1 or cVDPV within the last 24 months’ and extended the Temporary Recommendations under the IHR to reduce the risk of the international spread of poliovirus, effective 21 December 2023.