A child from the Roma community receives oral polio vaccine at a community health care centre in Mukachevo district, Ukraine, on 27 February 2023. © WHO/EURO

WHO/Europe has declared an outbreak of poliovirus in Ukraine, detected in October 2021, officially closed. The European Regional Commission for the Certification of Poliomyelitis Eradication endorsed the closure of the outbreak during its annual meeting on 8 September 2023. The country has achieved this milestone – stopping transmission of the virus that threatened the lives and futures of its children and preventing spread to other countries – in the face of the ongoing war.

The comprehensive outbreak response, initiated by the Ministry of Health of Ukraine in December 2021, faced multiple challenges since the end of February 2022, including massive population displacement, destruction of health-care infrastructure and disruption of logistical routes for medical product deliveries.

“Stopping the spread of poliovirus in the midst of a devastating war is a major achievement and a clear demonstration of the highest level of political commitment of the Government of Ukraine to the welfare of its population,” said Dr Hans Henri P. Kluge, WHO Regional Director for Europe.

“In the face of unprecedented challenges, the necessary steps taken by the Ministry of Health of Ukraine to prevent the spread of poliovirus within and beyond the borders of Ukraine are immensely commendable.”

The decision to close the outbreak was based on:

  • the recommendations of a poliovirus outbreak response assessment (OBRA) conducted by Global Polio Eradication Initiative (GPEI) partners, including WHO, in May 2023;
  • additional documentation provided by Ukraine in support of the ongoing surveillance, immunization and communication efforts since May; and
  • a comprehensive review of poliovirus surveillance and vaccination performance in the countries hosting the majority of the Ukrainian refugee population.

The outbreak was first detected in a young child in Ukraine in October 2021, following the importation of a poliovirus that had emerged in Pakistan and was previously detected in Tajikistan in 2021. A second child became paralysed in December 2021, and an additional 19 close contacts tested positive without developing symptoms.

“The Ministry of Health of Ukraine declared importation of this poliovirus a local public health emergency, and acted swiftly since its detection in close coordination with the global public health community,” said Dr Viktor Liashko, Minister of Health of Ukraine.

Dr Liashko continued, “The outbreak is now closed, but our work to prevent polio and other vaccine-preventable diseases in Ukraine continues despite all obstacles. As long as polio remains a threat globally, Ukraine will remain vulnerable. The Ministry of Health is committed to strengthening vaccine-preventable disease surveillance and working to achieve and sustain high routine immunization coverage nationwide to protect every child.”

What does it take to stop a polio outbreak?

In October 2021 the detection of poliovirus in Ukraine triggered the declaration of a public health emergency in affected oblasts, the creation of a response working group with technical support from GPEI and WHO specialists, and an immediate epidemiological investigation including contact tracing and environmental sampling at a summer camp, school and residences where the virus had been initially detected.

Health workers take a wastewater sample at a sewage site near Uzhgorod, Ukraine on 28 February 2023. © WHO/EURO

On 30 December 2021 the Ministry of Health approved an action plan in response to the outbreak that included, among other initiatives, an accelerated immunization catch-up campaign for children aged 6 months to 6 years who had not received the required doses through routine immunization.

The campaign began in mid-February 2022, but its scale and pace were significantly affected by the war in Ukraine. GPEI partners including WHO provided technical and operational support tailored to the context to build capacity and strengthen routine immunization services, disease surveillance, communication and transportation of samples to reference laboratories abroad.

Dr Jarno Habicht, WHO Representative in Ukraine, coordinated the WHO response within the country. “WHO and GPEI partners have been on the ground from day one, supporting Ukraine’s health authorities, medical and public-health professionals, laboratory staff, and communities to keep this virus from spreading,” he explained. “The excellent collaboration and perseverance of the local and international teams to protect children in the most difficult of circumstances has been truly inspiring.”

Despite the many challenges in implementing the national action plan for the outbreak response, no new detections of poliovirus were identified after December 2021. The OBRA conducted in May 2023 assessed the critical components of the outbreak response, such as the quality of surveillance (and thereby the risk of undetected poliovirus transmission), planning and coordination, the vaccination campaign, routine immunization performance, communication, and vaccine management. Based on the field assessment and review of the documentation, the OBRA concluded that poliovirus was no longer circulating in Ukraine.

The OBRA in Ukraine was followed by a comprehensive review of actions taken by Bulgaria, Czechia, Hungary, Poland, the Republic of Moldova, Romania and Slovakia. This was coordinated by WHO/Europe with financial support from the United States Agency for International Development (USAID).

The review assessed the actions to expand capacities to detect the virus, identify gaps in vaccination coverage and increase coverage of the local populations hosting Ukrainian refugees, and offer vaccination to refugees entering from Ukraine. This review, along with the additional information provided by Ukraine on actions implemented during the months following the OBRA, enabled WHO/Europe to declare the outbreak officially closed.

Mr Robb Butler, Director of the Division of Communicable Diseases, Environment and Health at WHO/Europe, stated, “Ukraine has been steadfast in recent years in its efforts to achieve and sustain high routine vaccination coverage, and within the realm of the European Immunization Agenda 2030, WHO/Europe will continue to support health authorities to prevent further outbreaks of vaccine-preventable diseases including polio, measles, diphtheria and many more.”

Mr Butler concluded, “Tremendous credit goes to the health professionals and parents who continue to make every effort to vaccinate children on schedule to protect them from the threat of polio and other diseases, even while navigating the daily realities and dangers of war.”

The Global Polio Eradication Initiative (GPEI) is extremely concerned about the unfolding effects of the current crisis in Ukraine on the country’s health system.  A functioning health system must be kept neutral and protected from all political or security issues affecting countries, to ensure that people have continued access to critical and essential care.

At the same time, we have seen time and again that large-scale population movements, insecurity and hampered access contribute greatly to the emergence and/or spread of infectious diseases, such as polio.

Ukraine is currently affected by a circulating vaccine-derived poliovirus type 2 (cVDPV2) outbreak, with the most recent case detected in January 2022 (with disease onset in December 2021).

A national supplemental polio immunization campaign targeting nearly 140,000 children throughout Ukraine who had not been vaccinated against polio began on 1 February 2022, but is currently paused, as health authorities have shifted focus towards emergency services. Surveillance to detect and report new cases of polio is also disrupted, increasing the risk of undetected spread of the disease among vulnerable populations. The GPEI is working to urgently develop contingency plans to support Ukraine and prevent further spread of polio.

The GPEI has a long history of working in a variety of complex environments, and will continue to adapt its operations to the reality on the ground, to the degree possible, without compromising on the safety and security of health workers.  At the same time, immunization and surveillance is being assessed in neighbouring countries, to minimize the risk and consequences of any potential infectious disease emergence/spread resulting from the current large-scale population movements.  It is critical that necessary resources are mobilized and made available to assist with the humanitarian needs, including relief, disease response/prevention efforts both in Ukraine and in neighbouring countries.

Boy receiving polio drops from a health worker, with his mother during a polio vaccination campaign in 2015. © WHO / Alex Shpigunov
Boy receiving polio drops from a health worker, with his mother during a polio vaccination campaign in 2015. © WHO / Alex Shpigunov

A poliomyelitis (polio) vaccination campaign for children aged 6 months to 6 years who missed routine polio doses in the past will begin in Ukraine on 1 February 2022. This catch-up campaign is part of a comprehensive response to stop an outbreak of poliovirus first detected in Ukraine in October 2021. This first stage will last 3 weeks and is expected to reach nearly 140 000 children throughout the country.

Years of low immunization coverage in Ukraine have created a large pool of unvaccinated or under-vaccinated children who are vulnerable to polio. While routine immunization coverage has gradually increased over the past 6 years, in 2020, only 84% of 1-year-olds received the required 3 scheduled doses of polio vaccines by 12 months of age.

The immediate goal of the campaign is to reach the WHO-recommended level of 95% vaccination coverage of eligible children.

Background

The polio outbreak in Ukraine was confirmed on 6 October 2021. Poliovirus (circulating vaccine-derived poliovirus type 2) was first isolated in a 17-month-old girl in the province of Rivne who developed acute flaccid paralysis. Analysis of all her contacts found that 7 household contacts (siblings) and 8 community contacts in Rivne as well as 4 cousins in the province of Zakarpattya (who had had contact with the girl’s siblings) also tested positive, but did not develop paralytic symptoms.

A second case with acute flaccid paralysis (a 2-year-old boy in the region of Zakarpattya) also tested positive for poliovirus, with onset of paralysis in December 2021.

The isolated strain of the virus found in both paralytic cases and their contacts is linked to a poliovirus in Pakistan, which was also the cause of several cases in Tajikistan in 2020–2021.

Comprehensive plan to stop the spread of poliovirus

Following an initial local vaccination campaign, conducted where the first case was detected, a comprehensive polio outbreak response plan was approved by the Ministry of Health in December 2021.

The first stage of the plan will provide inactivated polio vaccine (IPV) to children aged 6 months to 6 years who have not received the required number of doses. In the second stage, all children under the age of 6 will be vaccinated with oral polio vaccine (OPV), even if they have received all their scheduled vaccination doses. This is necessary to protect children from infection and to stop the circulation of the virus. Dates for the second stage are pending.

WHO/Shpigunov

A team of technical experts assessed Ukraine’s response to a polio outbreak and concluded that transmission of poliovirus has been interrupted. Nevertheless, the team remains concerned about significant gaps in immunization and surveillance that put Ukraine at high risk for new outbreaks.

“Thanks to the efforts of the Ministry of Health, health workers and parents, many more children are vaccinated against polio, and I commend them for their commitment,” said Dr Zsuzsanna Jakab, WHO Regional Director for Europe. “But these efforts do not stop now. The immunization gap persists and, if Ukraine does not continue vaccinating its children, this gap will expand for polio and other vaccine-preventable diseases to strike.”

High routine immunization coverage

Owing to low coverage, immunization gaps accumulated in Ukraine; it interrupted polio transmission with a campaign of three rounds of catch-up vaccination. High routine immunization coverage is a top priority for WHO, to ensure that another outbreak of polio or any other vaccine-preventable disease does not hit the country.

“We need to seize the momentum gained during the polio outbreak to strengthen Ukraine’s immunization programme, so that parents may exercise their right and responsibility to vaccinate their children,” said Dr Luigi Migliorini, WHO Representative in Ukraine.

With the United Nations Children’s Fund (UNICEF), WHO is supporting the Ministry of Health in making vaccines available to close the country’s immunization gap and protect against all vaccine-preventable diseases.

Recommendations of the expert team

An expert team from different United Nations agencies and partners assessed the polio-outbreak response over two weeks in five Ukrainian regions, at both oblast and rayon levels. Experts analysed the disease surveillance systems, supplementary immunization activities, and communications “, said Dr Patrick O’Connor, leader of the WHO assessment team.

As well as concluding that poliovirus transmission in Ukraine had been interrupted, the team recommended key actions to mitigate the risk of future outbreaks:

• increase political commitment for childhood immunization;

• re-establish high, uniform immunization coverage with polio vaccines;

• improve the communication skills of frontline health workers; and

• enhance surveillance for early detection of polioviruses.

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Girl proudly displaying her marked finger, indicating that she has been vaccinated against polio. © Unicef
Girl proudly displaying her marked finger, indicating that she has been vaccinated against polio.
© Unicef

In Ukraine, 2 cases of circulating vaccine-derived poliovirus type 1 (cVDPV1) have been confirmed, with dates of onset of paralysis of 30 June and 7 July 2015. The genetic similarity between the cases indicates active transmission of cVDPV1. Both are from the Zakarpatskaya oblast, in south-western Ukraine, bordering Romania, Hungary, Slovakia and Poland. One child was 4 years old and the other 10 months old at the time of onset of paralysis.

Ukraine had been at particular risk of emergence of a cVDPV, due to inadequate vaccination coverage. In 2014, only 50% of children were fully immunized against polio and other vaccine-preventable diseases.

Discussions are currently ongoing with national health authorities to plan and implement an urgent outbreak response. An outbreak response of internationally-agreed standard, as adopted by the World Health Assembly in May 2015, requires a minimum of three large-scale supplementary immunization activities with an appropriate oral polio vaccine, to begin within two weeks of confirmation of the outbreak and covering a target population of 2 million children aged less than five years, and the public declaration of the outbreak as a national public health emergency.

Circulating VDPVs are rare but well-documented strains of poliovirus that can emerge in some populations which are inadequately immunized. A robust outbreak response can rapidly stop such events. The emergence of cVDPV strains underscores the importance of maintaining high levels of routine vaccination coverage.

It is important that all countries, in particular those with frequent travel and contacts with polio-affected countries and areas, strengthen surveillance for AFP cases in order to rapidly detect any new virus importation or emergence and to facilitate a rapid response. Countries should also maintain uniformly high routine immunization coverage at the district level to minimize the consequences of any new virus introduction.

WHO’s International Travel and Health recommends that all travelers to polio-affected areas be fully vaccinated against polio. Residents (and visitors for more than 4 weeks) from infected areas should receive an additional dose of OPV or inactivated polio vaccine (IPV) within 4 weeks to 12 months of travel.

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