Wild poliovirus

WPV1 transmission continues to fall, with no new case since January 2021 when two WPV1 cases occurred, one each from Pakistan and Afghanistan, compared to 94 WPV1 cases during the same time period in 2020. Similarly from environmental surveillance, the overall proportion of specimens that are positive has reduced from almost 60% in 2020 to less than 15% in 2021 to date with no detection in Afghanistan since 23 February and only ten isolates in Pakistan since 31 March. The most recent detections in 2021 in Afghanistan were both the result of importation from Pakistan.

While the Committee noted the commendable progress being made, there is no room for complacency. The Committee recognised significant ongoing challenges and threats to front-line workers, including deaths of immunisation staff in Afghanistan and of supporting police officials in Pakistan.  Although surveillance is functioning well in most areas of the two endemic countries, recent isolation of long-chain or orphan viruses in both countries indicates a possibility of missed transmission in the hard-to-reach and high-risk population groups.  The ongoing inaccessibility in many provinces of Afghanistan coupled with increasing military conflict remains a major risk.  Around three million children were persistently missed in 2020 and 2021 so far, with around one million children in Southern Afghanistan missing out on vaccination for almost three years. Hence, the cohort of missed children continues to grow.  Progress in conducting mosque-based campaigns in non-government-controlled areas signals a hopeful path to addressing this gap.

There has been inconsistent vaccination campaign quality in critical areas of Pakistan and Afghanistan, including Karachi, Quetta Block and the Southern Region of Afghanistan.  The potential effects of COVID-19 including new variants in Afghanistan and Pakistan may cause interruption of polio eradication activities; mitigating this risk is the potential effect of lockdowns, travel restrictions and border closures on transmission rates of many infections including polio.

Circulating vaccine-derived poliovirus (cVDPV)

The number of cases of cVDPV2 in 2021 so far is 170 compared to the total cases in 2020 of 1069.

However, there have been no new emergences detected so far in 2021. In Afghanistan in 2021, all cVDPV2 cases occurred in inaccessible areas.  The total number of lineages detected in 2021 is 15 so far, compared to 36 in 2020, and 44 in 2019. This reduction may reflect refinement and modification of cVDPV2 outbreak management to lessen the risk of seeding new emergences. Both the newly infected countries since the last meeting (Gambia and Uganda) have resulted from the international spread. Based on analysis of isolates by genomic analysis, in the three months from January to March 2021, there have been eight episodes of international spread of cVDPV2. China has reported an outbreak of cVDPV3 due to local emergence, bringing the total number of infected countries to 31.

The roll-out of the novel OPV2 vaccine continues with seven countries having now implemented vaccination response rounds.  Four additional countries are verified as ready to use it while another seven countries are close to being verified.

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 as evidenced by recent infections in Gambia and Uganda following importation from a neighboring country. Experience in Egypt and Iran has demonstrated that countries with high RI and IPV coverage are also at risk of established cVDPV2 transmission, following importation.

Conclusion

Although heartened by the apparent progress, 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.  The Committee recognizes the concerns regarding the lengthy duration of the polio PHEIC, but concludes that the current situation remains risky, with clear ongoing risk of international spread and ongoing need for coordinated international responses. The Committee also recognised that the ongoing COVID-19 pandemic may have an adverse impact on polio surveillance and on immunisation activities, as will the gradual withdrawal of polio funds from some of the affected countries. The Committee considered the following factors in reaching this conclusion:

Rising risk of WPV1 international spread:

Based on the following factors, the risk of international spread of WPV1 appears to continue:

• the actual exportation from Pakistan into Afghanistan in the first quarter of 2021, despite border vaccination well re-established after the 2020 pause;
• the ongoing inaccessibility in many provinces of Afghanistan leading increasingly to highly susceptible populations which might lead to higher transmission; over three million children were missed in the October and November NIDs, and the cohort of missed children continues to grow quickly;
• the increasing civil war in Afghanistan with population movement increasing, including into Pakistan;
• ongoing vaccine hesitancy in Pakistan fueled by continued misinformation on social media regarding COVID-19 vaccines leading to higher numbers of missed children particularly in high-risk districts.

Rising risk of cVDPV2 international spread:

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

• the actual eight documented instances of cross border spread and two newly infected countries;
• the ever-widening gap in population intestinal mucosal immunity in young children since the withdrawal of OPV2 in 2016;
• the same factors regarding the COVID-19 pandemic as mentioned above;
• the population of inaccessible children in Afghanistan that appears to be driving transmission there.

Other factors include

• Weak routine immunization: Many countries have weak immunization systems that can be further impacted by various humanitarian emergencies including COVID-19, and the number of countries in which immunization systems have been weakened or disrupted by conflict and complex emergencies poses a growing risk, leaving populations in these fragile states vulnerable to outbreaks of polio.
• Lack of access: Inaccessibility continues to be a major risk, particularly in several countries currently infected with WPV or cVDPV, i.e. Afghanistan, Nigeria, Niger, and Somalia, which all have sizable populations that have been unreached with polio vaccine for prolonged periods.

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 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 the collection of the most recent positive environmental or other samples (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 the potential risk of international spread

WPV1                                                                                                         

Afghanistan                       (most recent detection 23 Feb 2021)

Pakistan                            (most recent detection 6 July 2021)

cVDPV1

Madagascar                       (most recent detection 11 Jun 2021)

Yemen                                (most recent detection 27 March 2021)

cVDPV3

China                                  (most recent detection 25 Jan 2021)

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 (i.e. > 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 (i.e. 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 (e.g. road, air, 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:

Afghanistan              (most recent detection 9 Jul 2021)

Benin                        (most recent detection 2 Apr 2021)

Burkina Faso            (most recent detection 9 Jun 2021)

Cameroon                (most recent detection 29 Sept 2020)

CAR                         (most recent detection 2 Oct 2020)

Chad                        (most recent detection 25 Nov 2020)

Rep Congo               (most recent detection 14 Apr 2021)

DR Congo                 (most recent detection 30 Apr 2021)

Côte d’Ivoire              (most recent detection 9 Oct 2020)

Egypt                         (most recent detection 8 Jun 2021)

Ethiopia                     (most recent detection 29 Apr 2021)

Gambia                      (most recent detection 9 Jun 2021)

Ghana                        (most recent detection 17 Sept 2020)

Guinea                       (most recent detection 1 Apr 2021)

Iran                            (most recent detection 20 Feb 2021)

(the Islamic Republic of)

Liberia                         (most recent detection 28 Jun 2021)

Mali                             (most recent detection 23 Dec 2020)

Niger                           (most recent detection 8 Dec 2020)

Nigeria                        (most recent detection 29 June 2021)

Pakistan                      (most recent detection 18 May 2021)

Senegal                       (most recent detection 14 Jun 2021)

Sierra Leone                (most recent detection 1 Jun 2021

Somalia                        (most recent detection 23 May 2021)

South Sudan                (most recent detection 10 Apr 2021)

Sudan                          (most recent detection 3 Dec 2020)

Tajikistan                      (most recent detection 26 Jun 2021)

Togo                             (most recent detection 9 Jul 2020)

Uganda                        (most recent detection 1 Jun 2021)

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 mOPV2 stockpile based on the recommendations of the Advisory Group on mOPV2.
• 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, according to the advice of the Advisory Group.

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

none                         (most recent detection 6 Aug 2020)

cVDPV

Myanmar                   (most recent cVDPV1 detection 9 August 2019)

Zambia                      (most recent cVDPV2 detection 25 November 2019)

Philippines                 (most recent detection 16 January 2020)

Angola                       (most recent detection 9 February 2020)

Malaysia                    (most recent detection 13 March 2020)

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 welcomed the substantial progress that has been made but warned that the situation in Afghanistan risked a rapid reversal of progress.  The Committee urged the polio programme to continue to discuss with all parties involved to ensure every missed child in inaccessible areas be quickly brought up to date with vaccines to avoid a sudden surge in cases, particularly as the high season commences. The Committee also urged donors and partners to continue their support, noting the beneficial use of polio assets during the pandemic and that a critical juncture had been reached:  decreasing funding by governments, partly as a result of the pandemic, risked all the hard-won gains being lost.

The Committee also welcomed the roll-out of novel OPV2 but was concerned to hear of delays in outbreak response, in some cases as countries preferred to wait for novel OPV2.  Polio outbreaks should continue to be met with a suitable sense of urgency, and response time generally needed to be reduced.  The Committee requested the polio programme to continue to assist countries to mount an emergency response with whichever vaccine formulation was available.

The Committee also warned of the ongoing effects of COVID-19, particularly on routine immunization, and possible future disruptions of supply and delivery of vaccines.  COVID-19 is likely to continue to have negative effects on all health programs and systems for some time to come, so the polio programme must continue to adjust its response on an ongoing basis to get over the remaining hurdles.

Based on the current situation regarding WPV1 and cVDPV, and the reports provided by affected countries, the Director-General accepted the Committee’s assessment and on 10 August 2021 determined that the situation relating to poliovirus 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 10 August 2021.