Post-38th IHR Emergency Committee Meeting on Polio Update

The thirty-eighth 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 20 March 2024 with committee members and advisers meeting 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 interruption and certification of WPV1 eradication by 2026 and interruption and certification of cVDPV2 elimination by 2028. Technical updates were received about the situation in the following countries: Afghanistan, Angola, Côte d'Ivoire, Indonesia, Liberia, Mozambique, Pakistan, Sierra Leone, South Sudan and Sudan.

Wild poliovirus

There have been two new cases of WPV1 in Pakistan reported in 2024, both cases were detected in Balochistan province (Chaman and Dera Bugti districts). The significant increase in environmental detections have been sustained with 125 positive samples in 2023 and 34 positive samples to date in 2024. These detections indicate the spread of WPV1 from the endemic zone of Afghanistan (East Region) to other regions in Afghanistan (Balkh, Kabul and Southern provinces centered on Kandahar) to the traditional reservoirs of Pakistan (Karachi, Peshawar and Quetta Block) and neighboring or transit districts.

Both countries have made progress towards interrupting transmission of the two surviving genetic clusters of WPV1 (the YB3C cluster is endemic in Pakistan and the YB3A cluster is endemic in Afghanistan). In 2023, Afghanistan reported six cases of WPV1 belonging to the YB3A cluster from the East Region of the country. The 62 environmental samples that were positive for WPV1 all belong to the YB3A cluster. In 2023, Pakistan reported six cases of WPV1, three WPV1 cases belong to its endemic YB3C cluster whilst the other three WPV1 cases belong to the YB3A cluster closely related to strains circulating in East Region of Afghanistan. Pakistan also detected 125 WPV1 isolates from environmental samples collected during 2023 of which 119 belong to the YB3A cluster and are closely related to the strains circulating in Afghanistan. There is evidence to suggest that some of the YB3A strains detected in Afghanistan in late 2023 were reintroduced into Afghanistan by returnees from Pakistan. The most recent YB3C detection was reported in October 2023. The number of environmental samples in Pakistan tested rose from 1199 in 2022 to 2182 in 2023. In Afghanistan, the number of samples decreased from 698 in 2022 to 521 in 2023 but maintained quality.

The WPV1 epidemiology reported by Afghanistan is incomplete. In late January, shipments, testing and related reporting of WPV1 samples in Afghanistan were suspended due to concern about the testing and notification of a positive WPV1 sample by the Regional Reference Laboratory (RRL) in Islamabad. Following outreach and collaboration, this sample has been referred to the Global Specialized Laboratory (GSL) in Atlanta USA for retesting and has now been confirmed as positive. On 18 March Afghanistan also reported 10 positive environmental samples collected in January. The shipment of samples to the RRL in Islamabad resumed on 15 March. It is estimated that the testing backlog of more than 1400 stool and wastewater samples will be cleared by mid-April 2024.

Both Afghanistan and Pakistan are implementing an intensive and synchronized campaign schedule focusing on improved vaccination coverage in the endemic zones and effective and timely response to WPV1 detections elsewhere in each country. At least 175 million vaccinations are planned for implementation in both countries between January and June 2024. Coverage in the East Region (Nangarhar, Kunar, Nuristan and Laghman) has been strengthened through increased supervision, oversight and monitoring as well as expanded to include children under 10 due to the age profile of the infected children and related historical accessibility challenges in the East Region. Vaccination coverage has also improved in the South Region (Hilmand, Kandahar, Uruzgan, Zabul and Nimrod) through intensified collaboration with humanitarian partners and other modalities but remains suboptimal with an estimated 200 000 children who remain unreached. Across south KP, efforts have focused on access improvement, higher quality surveillance and integrated vaccine delivery in selected Union Councils around North Waziristan and Bannu in particular, whilst enhancing operational coordination and community engagement. Outbreak response elsewhere in Pakistan has focused on the traditional reservoirs and the vaccination of mobile populations including those impacted directly or indirectly by the repatriation of undocumented migrants to Afghanistan.

In addition to seasonal movement patterns within and between both countries, this return of undocumented migrants from Pakistan to Afghanistan has compounded the challenges faced. More than 600 000 returnees have been recorded to date by IOM and UNHCR with estimates of up to 1 700 000 affected. The scale of the displacement increases the risk of cross-border poliovirus spread as well as spread within both countries. This risk is being managed and mitigated in both countries through vaccination at border crossing points and the updating of micro-plans in the districts of origin and return. The programme will continue to closely coordinate with IOM and UNHCR.

Twenty months have now elapsed since the last recorded WPV1 case in Mozambique with onset of paralysis on 10 August 2022. More than two years have now elapsed since the single WPV1 case reported in Malawi. Outbreak response assessments (OBRA) were conducted in Mozambique and Malawi in November 2023. In Mozambique, there are encouraging signs that imported WPV1 transmission has stopped but 12 months of complete surveillance data is not yet available. In Malawi, the OBRA team concluded that imported WPV1 transmission has most likely stopped. Geographic proximity means that the outbreak will be closed together rather than separately. Closure of the outbreak will be by the WHO African Regional office following review by the Regional Commission for Certification.

Circulating vaccine derived poliovirus (cVDPV)

There are five newly reinfected countries reporting cVDPV2 since the last meeting: Angola, Liberia, Senegal, Sierra Leone and South Sudan. In South Sudan, there has been a new emergence; in the other four countries, reinfection has been due to importation events with Angola importing two different cVDPV2 emergence groups. Furthermore, a new cVDPV2 has been detected in Mozambique. In Côte d'Ivoire, there has been a rapid increase in environmental samples that have tested positive for cVDPV2.

There have been new emergences of cVDPV2 detected in Sudan and Mozambique. In Indonesia there has been a recurrence of cVDPV2, after an interval of 10 months with no detections, with three new cases and an environmental sample testing positive, all with links to Madura Island in East Java. Additionally, there has been a VDPV1 detected in Central Papua which is under further investigation.

There has been no new country reporting cVDPV1.

In 2023, there have been 522 cases confirmed with cVDPV, of which 388 are cVDPV2 and 133 are cVDPV1. The trend is downwards with 882 cVDPV cases in 2022 of which 689 were cVDPV2 and 193 were cVDPV1. Of these 522 cases, 223 (43%) have occurred in the DR Congo. Algeria, Angola, Botswana, Cameroon, Rep. Congo, Egypt, Malawi, Senegal and Sudan have detected cVDPV in the environment but have not detected any cases. In 2024, only Nigeria has detected cases, while Algeria, Angola, Côte d'Ivoire, Egypt, Liberia, Sierra Leone and Sudan have detected cVDPV in the environment. Most countries have been infected by imported viruses, while three countries, Zimbabwe, Indonesia and Israel have been infected despite not having used any type of OPV2 prior to detection of cVDPV2.

In 2023, the number of separate cVDPV2 emergence groups detected was 25, of which eight were new emergences, of which six originated from nOPV2. This compares to 19 emergence groups detected in 2022, 28 in 2021, 35 in 2020, and 44 in 2019. There have now been 14 nOPV2 derived emergence groups since 2021.

The committee noted that in the African Region, which now uses novel OPV2 exclusively, there has 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, including cVDPV2, 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.

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 and under-immunized children and population displacement. These factors are most evident in northern Yemen, northern Nigeria, south central Somalia and eastern DR Congo, but also in northern Mozambique, Burkina Faso, Mali, South Sudan and Sudan.

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 the extension of 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 and 2024;
• 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 a number of provinces of Afghanistan;
• the large pool of unvaccinated 'zero dose' and underimmunized 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; and
• any setback in Afghanistan poses a risk to the programme in Pakistan due to high population movement.

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 re-infected countries such as Angola, Liberia, Senegal and Sierra Leone;
• the new emergence of cVDPV2 in South Sudan, which whole genome sequencing (WGS) indicates the origin of the virus is novel OPV2, despite that the vaccine has never been used in the country. However, South Sudan shares many land borders with countries that have used novel OPV2 in the years 2022 – 2023, including Ethiopia, Kenya, Uganda, DR Congo and CAR;
• 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; and
• 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

WPV1

cVDPV1

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 no longer polio infected, but 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 noted that the genetic diversity of WPV1 continues to shrink in the single epidemiological block of Afghanistan and Pakistan, and that case numbers of cVDPV1 and cVDPV2 continue to decrease globally, for example in Madagascar, which following intensive vaccine response appears to have halted transmission since September 2023. As demonstrated by environmental surveillance, international spread continues, emphasizing the need to further strengthen cross border collaboration in all areas of polio eradication such as surveillance and data sharing, not only in synchronization of case response immunization rounds and border vaccination posts.

The Committee recognizes the concerns regarding the lengthy duration of the polio PHEIC and the importance of exploring alternative measures. 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, notes and appreciates the increased use of women health care workers in campaigns, 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 was concerned by the pause in testing and reporting of polio test results during January and February 2024 that has led to a large backlog of specimens and heightened the risk of undetected transmission and late detections of outbreaks. Given the historically very high standards achieved for surveillance sensitivity and timeliness of detection, avoiding any further recurrence is essential to ensure the timely identification and assessment of risk to inform continued effective vaccination response in Afghanistan. The committee urges all countries to ensure that polio detection and outbreak response is as timely as possible.

The committee noted that environmental surveillance had played a significant role in detection of the new outbreaks detected in several countries, such as Angola, Liberia and Sierra Leone and encouraged countries to continue to work to improve the quality of ES to maximize the benefits of its implementation.

The committee was concerned to hear about the ongoing supply issues regarding novel OPV2 and noted the plans to obtain a second supplier. The committee considered that the securing of vaccine supply was a critical issue, and that there should be planning to ensure a more robust vaccine supply beyond admission of a new supplier. While encouraging countries to declare public health emergencies following detection of a new outbreak, such crucial actions need to be supported by the GPEI in ensuring vaccine availability.

Many of the cVDPV infected countries remain conflict affected, disrupting routine immunization. Nevertheless, steps should be taken to increase coverage of the second dose of IPV, to prevent children from being crippled. Front line workers need to be protected from harm during the course of their duties, as the interplay between insecurity, poor polio vaccine coverage, and risk of cVDPV is clear.

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 28 March 2024 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 28 March 2024.