Circulating vaccine-derived poliovirus type 3 – Israel - ISS-G20 Laboratorium Repository

Outbreak at a glance

WHO was notified on 7 March 2022 of the detection of circulating vaccine-derived poliovirus type 3 (cVDPV3) in an unvaccinated child from Jerusalem city. Investigations (including environmental, epidemiological and virological) are ongoing to determine the origin of cVDPV3 and the scope of circulation. As of 15 April, a total of seven VDPV3 positive have been confirmed, including the index case and six asymptomatic children. As an immediate response, immunization activities with inactivated polio vaccine (IPV) and catch-up vaccination were initiated in Jerusalem, and a bivalent oral polio vaccine (bOPV) campaign started on 4 April 2022 in Jerusalem district which has been extended to the entire country as of 13 April. Given the high immunization coverage and robust surveillance system in the country, the risk of national spread is considered ‘moderate’.

Description of outbreak

On 7 March 2022, the International Health Regulations (IHR) National Focal Point (NFP) for Israel notified WHO of the detection of cVDPV3 in the country. According to the notification, cVDPV3 virus was isolated from an acute flaccid paralysis (AFP) case, in an unvaccinated child aged 3 years and 9 months, from the city of Jerusalem. The case had onset of paralysis on 17 February 2022. The isolated virus has 17 nucleotide changes from Sabin 3 (vaccine strain) and is genetically linked to a cluster of VDPV3 previously detected from environmental samples from Jerusalem and Bethlehem city, collected between September 2021 to January 2022. These vaccine-derived poliovirus isolates, previously classified as ambiguous, have now been reclassified as circulating.

As of 15 April, a total of seven VDPV3 positive have been confirmed, including the index case and six asymptomatic children. Of these seven children, only one had incomplete polio immunization while the other six were unvaccinated.

There were also an additional two children where VDPV3 was detected using in-house molecular techniques. Further confirmation is ongoing.

According to the routine immunization estimates provided by the IHR-NFP for Israel, the third dose of inactivated poliovirus (IPV) and first dose of oral polio vaccine (OPV) coverage in Israel was estimated to be 97.6% and 88.3% respectively in 2020.

Epidemiology of Poliomyelitis

Poliomyelitis (polio) is a highly infectious viral disease that largely affects children under five years of age. The virus is transmitted by person-to-person and spread mainly through the fecal-oral route or, less frequently, by a common vehicle (e.g., contaminated water or food) and 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. The virus enters the body through the mouth and multiplies in the intestine.  It then invades the nervous system. Up to 90% of those infected are either asymptomatic or experience mild symptoms and the disease usually goes unrecognized. In symptomatic cases, initial symptoms include fever, fatigue, headache, vomiting, stiffness in the neck, and pain in the limbs. These symptoms usually last for 2–10 days and most recovery is complete in almost all cases.  However, in the remaining 10% of cases, the virus causes paralysis, usually of the legs, which is most often permanent.  Paralysis can occur as rapidly as within a few hours of infection.  Of cases with paralysis, 5-10% die when their breathing muscles become immobilized.

The virus is shed by infected people (usually children) through faeces, where it can spread quickly, especially in areas with poor hygiene and sanitation systems.

There is no cure for polio; it can only be prevented by immunization.

• Local health authorities are conducting environmental, epidemiological and virological investigations, to determine the source and origin of the isolated virus, and the potential risk of further spread associated with it. Similar investigations are ongoing in the occupied Palestinian territory.
• An IPV and OPV polio catch-up vaccination was initiated for children aged six weeks to 17 years (inclusive). On 4 April, bOPV campaign was launched, focusing on Jerusalem district.  As of 13 April, the bOPV campaign has been extended to the entire country. 

Given the high level of vaccination coverage and robust surveillance system in Israel, the risk of further spread in the country, and in the occupied Palestinian territory, is likely to be moderate, as immunization gaps persist in certain high-risk areas/population groups.

WHO currently assesses the risk of further international spread associated with this cVDPV3 detection as low due to high population immunity, robust AFP surveillance, and existing response capacity. Investigation and response activities are being coordinated between the public health authorities of Israel and occupied Palestinian territory, and between WHO European and Eastern-Mediterranean Regional Offices .

Vaccination:

• There is currently no treatment for polio; it can only be prevented by immunization. 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.
• 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.

Surveillance:

• 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.

International Health Regulations:

• 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 Public Health Emergency of International Concern (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 travelers.
  • Ensure such travelers 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 travelers 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.
  • 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.

International travel or trade

• WHO advises against any restrictions on travel or trade with Israel, based on the currently available information

Entire content available on: https://www.who.int/emergencies/disease-outbreak-news/item/circulating-vaccine-derived-poliovirus-type-3---israel