Circulating vaccine-derived poliovirus type 2 (cVDPV2) - Indonesia

17 April 2023

Outbreak at a glance

On 17 March 2023, the Indonesia Ministry of Health notified WHO of the detection of a circulating vaccine-derived poliovirus type 2 (cVDPV2) in a 48-month-old female with acute flaccid paralysis (AFP), from Purwakarta district in West Java province. Field investigations were immediately launched by local and national public health authorities, with support from partners of the Global Polio Eradication Initiative (GPEI). Two rounds of immunization with novel OPV2 have been planned to cover children below five years of age, regardless of their prior vaccination status. The first round was implemented in April 2023. 

Description of the outbreak

On 17 March 2023, the Indonesia Ministry of Health notified WHO of the detection of a circulating vaccine-derived poliovirus type 2 (cVDPV2) in a 48-month-old female with acute flaccid paralysis (AFP), from Purwakarta district in West Java province. The case had the onset of paralysis on 16 February 2023. The girl had not received any previous doses of oral poliovirus vaccine (OPV) or inactivated poliovirus vaccine (IPV). A stool specimen was collected on 21 February 2023 and was confirmed to be cVDPV2 on 14 March 2023. Genetic sequencing results showed that the isolate has undergone 30 to 31 nucleotide changes from vaccine strains. The results of whole genome sequencing are pending. The patient and her parents had no travel history within the month before the onset of AFP; however, during this period, the household had received visitors including relatives from another village. 

A total of four confirmed cases of VDPV2 have been reported in Indonesia since November 2022. This includes three cases of circulating VDPV2 (cVDPV2) with acute flaccid paralysis (AFP) in Aceh province and one in West Java province. Additionally, four healthy children in Aceh province were confirmed to have cVDPV2 on 25 November 2022. The poliovirus was identified as being from the same emergence group as the cases reported in Aceh in 2022 and hence classified as cVDPV2 but is divergent from the Aceh viruses, signifying potentially missed transmission. A rapid risk assessment was conducted for the outbreak in Aceh in November 2022, which assessed the risk at the national level as high, regional level as moderate and global level as low.  

The administrative coverage of the bivalent oral polio vaccine (bOPV4) between 2018 and 2022 in West Java ranged from 88% to 102%, while coverage of inactivated polio vaccine (IPV) ranged from 26% to 106%. Vaccination coverage rates for bOPV and IPV were also above 90% in a catch-up campaign in West Java. Coverage with bOPV in the Purwakarta district has been consistently high between 2018 and 2022, ranging from 94% in 2020 to 104% in 2021; however, coverage with IPV decreased to 26% in 2020 before increasing to 80% in 2021, and reaching 100% in 2022.  

However, a pocket of unvaccinated children (for either bOPV and IPV) remains in West Java, which is mainly related to a lack of understanding of the importance of immunization by parents, concerns about the safety of the vaccines (including fever following immunization, receiving multiple injections and as a result of other sources of misinformation) and religious beliefs.

Epidemiology of Poliomyelitis

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 person-to-person, 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. 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 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 this virus 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, should be classified as ‘circulating’ vaccine-derived poliovirus type 2 (cVDPV2). 

Public health response

  • Following confirmation of the case in West Java, field investigations have been completed by the Ministry of Health, with support from WHO, UNICEF, and other partners, including an active search for AFP cases targeting at least 200 households and a review of hospital records.
  • Faecal samples have been collected from 30 healthy children, of which six samples were identified as VDPV2, which confirms that the virus was already circulating.
  • Two rounds of immunization with novel OPV2 have been planned to vaccinate a total of 3 984 797 children between 0 to 59 months in all 27 districts in West Java. The first round started on 3 April 2023. A cumulative coverage of 85.6% has been achieved in West Java in the first round as of 11 April 2023. The second round is planned for the third week of May.
  • Following the outbreak in Aceh on 25 November 2022, two rounds of supplementary immunization activities (SIAs) with nOPV2 were held in Aceh province for children aged 12 years and younger, starting on 28 November 2022. The cumulative coverage of 96% was achieved in the first and second rounds.
  • SIAs with nOPV2 in Aceh neighboring North Sumatra province started on 13 February 2023 and are ongoing. Currently, coverage with the first round among those aged 0-59 months is 93%. The total target population for the two provinces combined is 2 564 594. This number has met the minimum number target to be covered during SIAs for cVDPV2 outbreak control, as recommended by WHO.

WHO risk assessment

WHO assesses the risk to be high at the national level. Despite Indonesia having a strong capacity to respond to poliovirus outbreaks and West Java having a moderate to strong outbreak response capacity to interrupt transmission, there is a high susceptibility of the population to poliovirus type 2 after switching from trivalent to bivalent OPV; sub-optimal IPV coverage in Aceh, West Java and several other provinces in Indonesia; high population mobility between West Java and other provinces within Indonesia; and reluctance to vaccinate among at-risk populations. The outbreak in Indonesia poses a moderate regional risk and a low risk globally.

The detection of cVDPVs highlights the importance of maintaining high levels of routine vaccination coverage everywhere to minimize the risk and consequences of the circulation of any poliovirus, as well as the need to ensure quality surveillance for early detection of any poliovirus.

WHO advice

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 and commence planned expansion of environmental surveillance 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.

WHO’s International travel and health recommends that all travellers to polio-affected areas be fully vaccinated against polio.

As per the advice of an Emergency Committee convened under the International Health Regulations (2005), the international spread of poliovirus remains 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 i) declare the outbreak as a national public health emergency; ii) encourage residents and long-term visitors to receive a dose of IPV four weeks to 12 months prior to international iii) encourage residents and long-term visitors to receive a dose of IPV four weeks to 12 months prior to international travel iv) further intensify efforts to increase IPV immunization coverage, including sharing coverage data, and v) further intensify efforts to increase IPV immunization coverage, including sharing coverage data.

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

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

Further information