Announcement

**Shiloh** · August 22, 2025, 02:44 PM

Source: https://www.who.int/emergencies/dise...em/2025-DON578

Circulating vaccine-derived poliovirus type 1 - Israel
20 August 2025
Situation at a glance
On 4 August 2025, Israel notified WHO of a circulating vaccine-derived poliovirus type 1 (cVDPV1) outbreak. Between February and July 2025, nine genetically linked virus isolates were found in environmental samples from seven sites, mainly in Jerusalem and the Central Region. No human cases of paralytic polio have been reported. Israel discontinued routine use of the bivalent oral polio vaccine in March 2025 but continues using inactivated polio vaccine (IPV) as part of the country’s routine immunization schedule. WHO and partners of the Global Polio Eradication Initiative are supporting national and subnational authorities. WHO assesses the risk of international spread of this cVDPV1 outbreak in Israel as low, due to strong overall immunity, surveillance, and response systems. However, the virus is circulating in under-vaccinated, vaccine-sceptic communities with ties to similar groups abroad, posing a potential risk for further spread.

Description of the situation

On 4 August 2025, WHO received an International Health Regulations notification from the IHR National Focal Point (NFP) for Israel reporting the declaration of a circulating vaccine-derived poliovirus type 1 (cVDPV1) outbreak in the country. Between February and July 2025, nine genetically related VDPV1 isolates were detected in environmental samples collected from seven sampling sites, four of which are geographically non-overlapping in the Jerusalem district and Central Region. Laboratory analyses and whole-genome sequencing (WGS) indicate that these viruses are genetically linked to each other and to multiple Sabin-like viruses isolated from environmental samples since October 2024. As of 8 August 2025, cVDPV1 has been detected only in environmental samples, with no paralytic cases reported at this stage. However current evidence supports classification of this event as an outbreak of cVDPV1 with sustained community transmission.

Prior to this outbreak a Sabin-like type 1 virus (SL1), related to SL1 viruses detected in environmental surveillance, was the cause of an acute flaccid paralysis (AFP) case in an unvaccinated 17-year-old male from Jerusalem that was reported on 23 December 2024 and classified as vaccine-associated paralytic poliomyelitis (VAPP).

Israel discontinued routine use of the bivalent oral polio vaccine (bOPV) in March 2025 but continues to administer four doses of inactivated polio vaccine (IPV) as part of the routine immunization schedule up to 12 months of age. The WHO/UNICEF Estimates of National Immunization Coverage for three doses of IPV in 2024 was 98%. However, vaccination coverage in Jerusalem is notably lower and below WHO’s recommended coverage threshold, which is necessary to maintain sufficient population immunity and prevent poliovirus transmission.

Epidemiology

Polio is a highly infectious disease that largely affects children under five years of age, causing permanent paralysis (approximately 1 in 200 infections) or death (2-10% of those paralyzed).

The virus is transmitted from person-to-person, mainly through the fecal-oral route or, less frequently, by contaminated water or food. The virus multiplies in the intestine, from where it can invade the nervous system and cause paralysis. The incubation period is usually 7-10 days but can range from 4-35 days. Up to 90% of those infected are either asymptomatic or experience mild symptoms and the disease usually goes unrecognized.

Vaccine-derived poliovirus is a well-documented strain of poliovirus mutated from the strain originally contained in OPV. OPV contains a live, weakened form of poliovirus that replicates in the intestine for a limited period, thereby developing immunity by building up antibodies. On rare occasions, when replicating in the gastrointestinal tract, OPV strains can genetically change and may spread in communities that are not fully vaccinated against polio, especially in areas where there is poor hygiene, poor sanitation, or overcrowding. The lower the population's immunity, the longer vaccine-derived poliovirus survives and the more genetic changes it undergoes.

In very rare instances, the vaccine-derived virus can genetically change into a form that can cause paralysis as does the wild poliovirus – this is what is known as a vaccine-derived poliovirus (VDPV). The detection of VDPV in at least two different sources and at least two months apart, that are genetically linked, showing evidence of transmission in the community, is classified as cVDPV. Similar to wild poliovirus, cVDPVs can be of three types (1,2 or 3), the current outbreak in Israel is due to cVDPV1.

Public health response

Enhanced AFP and environmental surveillance to detect further transmission are ongoing.
Under the Ministry of Health, a multi-disciplinary emergency response team (ERT) was established to support the control of outbreaks of cVDPV3 in 2022 followed by cVDPV2 in 2023 and this ERT continues to operate for this current cVDPV1 outbreak.
Investigations are ongoing to assess the scale of local circulation and the necessary responses where relevant.
Partners of the Global Polio Eradication Initiative, including the WHO European Regional Office, are supporting national and subnational authorities.
Targeted immunization campaigns with IPV have been ongoing since 2022, focusing on under-immunized communities. These campaigns are currently being intensified alongside measles vaccination efforts to maximize coverage. To enhance vaccine acceptance, the campaigns are supported by tailored, community-specific communication strategies.
Community- sensitive communication strategies are being developed with tailored messages to reduce the vaccine hesitancy and increase uptake.

WHO risk assessment

The international spread of poliovirus was declared a Public Health Emergency of International Concern (PHEIC) by the Director-General of the WHO on 5 May 2014, and most recently, the PHEIC declaration was extended on 28 July 2025. The outbreaks of cVDPV in Israel are covered by the original PHEIC declaration.

There is a high level of vaccination coverage and a robust surveillance system in Israel, however, the risk of further spread in the country is likely to be moderate as immunization gaps persist in known high-risk areas/population groups. Local health authorities are conducting field, epidemiological and virological investigations to better understand the situation and the likely risk of spread. Israel discontinued the use of bOPV in March 2025. The routine immunization schedule includes four doses of IPV-containing vaccine until the age of 12 months and a fifth dose during the second year of primary school.

In 2024, a total of 11 cVDPV1 cases were reported, ten in the Democratic Republic of the Congo and one in Mozambique. Despite no cVDPV1 case detection for the past 10 months, continued low routine immunization and IPV coverage in several countries and associated immunity gap, indicate continued risk of cVDPV1 emergence.

WHO currently assesses the risk of international spread associated with this cVDPV1 detection as low due to high overall population immunity, robust poliovirus surveillance, and response capacity. However, the potential for spread exists, taking into account the fact that circulation is likely occurring in the vaccine-sceptic under vaccinated communities with known close ties to similar communities in other countries. An example of this being the 2022-2023 multi-country circulation of cVDPV2 in the UK, USA, Canada and Israel.

WHO advice

The polio vaccine, given multiple times, can protect a child for life. WHO advises that every country should seek to achieve and maintain high levels of coverage with polio vaccine in support of the global commitment to eradicate polio. WHO recommends that all those who travel to or live in polio-affected areas should be fully vaccinated against polio in compliance with the national schedule. Population pockets with low immunity against polio should be prioritised for targeted interventions to boost immunity and reduce the risk of sustained transmission and spread.

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

As per the advice of the Emergency Committee convened under the International Health Regulations (2005), efforts to limit the international spread of poliovirus remain a PHEIC. Countries affected by poliovirus transmission are subject to Temporary Recommendations. To comply with the Temporary Recommendations issued under the PHEIC, any country infected by poliovirus should declare the outbreak as a national public health emergency, consider vaccination of all international travellers, ensure such travellers are provided with an international certificate of vaccination, restrict at the point of departure the international travel of any resident lacking documentation of appropriate polio vaccination, intensify cross-border efforts to substantially increase vaccination coverage of travellers, and intensify efforts to increase routine immunization coverage. Any country subject to the temporary recommendation maintains the measures described above until the following criteria have been met:

At least six months have passed without new infections; and
There is documentation of the full application of high-quality eradication activities in all infected and high-risk areas.

In the absence of such documentation, the measures should be maintained until the state meets the above assessment criteria for being no longer infected.

The latest epidemiological information on cVDPVs is updated on a weekly basis.

WHO does not recommend any travel and/or trade restrictions to Israel based on the current information available for this event...

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