the risk of international spread of poliovirus still remains a Public Health Emergency of International Concern

Wild poliovirus

The committee noted that there has been one new case of WPV1 in Pakistan since the last meeting, bringing the total to two in 2023. Both cases occurred in Bannu district in Khyber Pakhtunkhwa (KP) province. There have been 15 environmental surveillance positive samples in 2023. Although the action plan in southern KP has resulted in 160,000 more children being vaccinated, the context remains challenging, including 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 large number of children. Except for south KP, the historic reservoirs in Pakistan are no longer endemic, but recent positive environmental samples in Peshawar and Karachi underline that the risk of an outbreak continue.

In Afghanistan since the last meeting, there have been five new WPV1 cases reported, all from Nangarhar province. The cases occurred in five different districts and had onsets between 12 April – 18 May 2023. However, there have been 32 positive environmental samples to date in 2023, all in the eastern region, except for one site in Kandahar in the southern region and one from Balkh in the north. Although the number of positive samples in Afghanistan has increased in 2023 compared to the year 2022, this was in part due to more intensive surveillance in the country, with more sites being sampled and increased frequency of testing. The numbers of missed children are steadily decreasing and population immunity is improving. The programme is implementing high quality campaigns but the quality threshold will have to be increased further and sustained. A recent environmental detection in Kandahar in the South region is a public health emergency with a significant risk of a large outbreak because house-to-house campaigns in the South have not been authorized. Any setback in Afghanistan poses a risk to the programme in Pakistan due to high population movement.

Since the detection of WPV1 in Africa in February 2022, an effective coordinated response across Malawi, Mozambique, Tanzania, Zambia and Zimbabwe has been implemented.  Twenty-one rounds of campaigns have been conducted across this block, and the response has seen campaign quality continue to improve. It is now 12 months since the last case was detected in Mozambique on 10 August 2022. However, the committee noted that GPEI outbreak response assessments which were conducted in October 2022 in Malawi and in November 2022 in Mozambique to review progress concluded that ongoing transmission could not be ruled out in either country, due to gaps in polio surveillance and suboptimal coverage in immunization campaigns. Based on Lot Quality Assurance Sampling, campaign quality was less than the target 90% in Malawi, Mozambique, Zambia and Zimbabwe in the most recent rounds.

In 2023, there are only two genetic clusters of WPV1 identified, compared to three in 2022 and five in 2021. However, there have been multiple chains of transmission within these two genetic clusters, detected primarily in the endemic zones of Eastern Afghanistan and South KP of Pakistan, including an extreme orphan virus, indicating some gaps in surveillance. The Global Polio Laboratory Network plans to perform a thorough review of genetic characteristics and classification of WPV-1 by the end of 2023 and its findings will be shared with the Emergency Committee, when available.

Circulating vaccine derived poliovirus (cVDPV)

The number of cVDPV2 cases is declining and the geographic concentration is more focused, with modest reduction in the number of provinces and districts . 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 emergences. 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. The committee noted that in the African Region, which now uses novel OPV2 exclusively, there have been a total of eight new cVDPV2 emergences detected that have emerged from novel OPV2 use. However, novel OPV2 is retaining its enhanced genetic stability compared to Sabin OPV2, with most isolates analyzed through whole genome sequencing indicating no or minimal changes in genetic structure of novel OPV2. Only 2% of all isolates reported so far have shown evidence of losing key genetic modifications that reduce neurovirulence due to recombination, versus the expected 75% for Sabin OPV2.

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 expected to increase for the rest of the year.  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 in the context of the WPV1 outbreak in southern Africa, as it highlights gaps in population immunity to type 1 polioviruses including WPV1.

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 DR 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

Although encouraged by the reported progress, 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:

• the ongoing transmission in eastern Afghanistan with cross border spread into Pakistan;
• the large pool of unvaccinated ‘zero dose’ children in southern Afghanistan constitutes an ongoing risk of WPV1 re-introduction into the southern region;
• the importation of WPV1 from Pakistan into Malawi and Mozambique, noting that the exact route of the virus  remains unknown;
• sub-optimal immunization coverage achieved during campaigns in southeastern Africa, in Malawi, Mozambique, Zambia and Zimbabwe, meaning there may be insufficient population immunity to halt transmission;
• although surveillance has improved, some gaps in the outbreak response zone means that such transmission may be missed;
• pockets of insecurity and inaccessibility 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 ongoing outbreaks of cVDPV1 and cVDPV2 in eastern Democratic Republic of the Congo, which has caused international spread to neighbouring countries;
• the large outbreaks of cVDPV1 particularly in DR Congo and Madagascar and the insufficient number and quality of bOPV immunization response campaigns to date;
• the long distance spread by air travel of cVDPV2 between Israel, the United Kingdom, the USA, and Canada;
• the ever-widening gap in global population intestinal mucosal immunity in young children in many countries since the withdrawal of OPV2 in 2016;
• insecurity and inaccessibility in those areas that are the primary sources of cVDPV transmission.

Other factors include

• Weak routine immunization: Many countries have weak immunization systems that were further impacted by the COVID-19 pandemic but are gradually recovering. These services can be further affected by humanitarian emergencies including conflict, and protracted complex emergencies pose a continued risk, leaving populations in these fragile areas vulnerable to polio outbreaks.
• Lack of access: Inaccessibility continues to be a risk, particularly in northern Yemen and south central Somalia, which have sizable populations that have been unreached with polio vaccine for extended periods of more than a year, but violence remains an issue for campaign workers in several areas, including in Pakistan.

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

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 considered vulnerable for a further 12 months.  After this period, the country will no longer be subject to Temporary Recommendations, unless the Committee has concerns based on the final report.

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.
• 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 IPV immunization coverage, including sharing coverage data.
• 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 infected by WPV1 or cVDPV but which remain vulnerable to re-infection by WPV or cVDPV

WPV1

cVDPV

These countries should:

• Urgently strengthen routine immunization to boost population immunity.
• Enhance surveillance quality, including considering introducing 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.
• At the end of 12 months without evidence of reintroduction of WPV1 or new emergence and circulation of cVDPV, provide a report to the Director-General on measures taken to implement the Temporary Recommendations.

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, and encourages further discussion regarding these alternatives.  Nevertheless, 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.

Noting the acute humanitarian crises still unfolding in Afghanistan, the committee strongly encouraged 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 Committee noted with concern the new conflict areas in Sudan and West Africa that are disrupting health services and creating a new refugee crisis in neighboring countries. This situation must be closely monitored, as many of the neighboring countries already have cVDPV outbreaks resulting from low essential immunization coverage. More generally, noting the negative impact that the COVID-19 pandemic has had on essential immunization coverage in many of the polio affected countries, the committee stressed the importance of restoring essential immunization coverage. The committee recognized that border vaccination may not be feasible at very porous borders between some affected African countries but was concerned by the lack of synchronization and cross border coordination in Africa. The committee is concerned by conflicts and insecurity in many of the infected countries as such circumstances allows the polioviruses to elude control in countries such as Yemen, Nigeria, Dr Congo, Mozambique and Sudan.

The emergency committee noted that Madagascar has not yet declared the polio outbreak as a national public health emergency. There is continued cVDPV1 transmission in the country for several years, indicating that the vaccination response did not achieve the quality required to stop the polio outbreak.

Overall, the committee once again noted that many of the members states affected by WPV1 or cVDPV outbreaks hove either low overall coverage or low subnational coverage. The committee was gravely concerned by the lengthy outbreak in Madagascar, and the lack of timely and high quality response.

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.

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 23 August 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 no longer infected by WPV1 or cVDPV, but which remain vulnerable to re-infection by WPV or cVDPV’ and extended the Temporary Recommendations under the IHR to reduce the risk of the international spread of poliovirus, effective 23 August 2023.