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Polio Highlight

FAQ #3 When do countries need to introduce IPV and switch to bOPV?

When do countries need to introduce IPV and switch to bOPV?

OPV type 2 withdrawal would be achieved by switching from trivalent OPV (tOPV) to bivalent OPV (bOPV) (containing only types 1 and 3 poliovirus) in routine immunization programs. The World Health Organization’s (WHO) Strategic Advisory Group of Experts on immunization (SAGE) has called for a global withdrawal of type 2-containing OPV during 2016. This sets the stage for ending bOPV use entirely in 2019-2020. As a risk mitigation measure, SAGE recommends that prior to the ‘tOPV-bOPV switch’ all countries that currently use only OPV in their routine immunization programs introduce at least 1 dose of IPV into their routine schedules (i.e., by the end of 2015).


Why should countries introduce IPV prior to the tOPV-bOPV switch?

The withdrawal of OPV type 2 would leave a gap in population immunity against type 2 poliovirus. Thus, immediately following global withdrawal of OPV type 2, countries that have not introduced IPV would be at an increased risk of outbreaks in the case of reintroduction of a type 2 virus. A reintroduction or emergence of circulating vaccine-derived poliovirus type 2 (cVDPV2) could potentially result in a substantial polio outbreak or even re-establishment of global transmission.  Such an outbreak could be rapidly interrupted through mOPV type 2. Vaccinating the population with IPV through routine immunization would lessen the risk that reintroduction would lead to sustained transmission.  If reintroduction of type 2 polioviruses does occur post-eradication, having a population that has received IPV would also facilitate rapid control through targeted use of mOPV type 2.

FAQ #2 Why will countries need to switch from tOPV to bOPV?

Why will countries need to switch from tOPV to bOPV?

There are three types of wild poliovirus (WPV) - type 1, 2 and 3 - each of which is targeted by a different component of the trivalent oral polio vaccine (tOPV).

Live attenuated vaccines are very effective against the wild virus, but in very rare cases can lead to paralysis. There are two ways this can occur:

  • Vaccine Associated Paralytic Poliomyelitis (VAPP): At a global level for every birth cohort of 1 million children in OPV-only using countries, there are 2-4 cases of VAPP.  This translates to an estimated 250 – 500 VAPP cases globally per year.  Of these, about 40% are caused by OPV’s type 2 component. In the Region of the Americas, the VAPP risk is 1 case per 7.68 million doses administered.
  • Circulating Vaccine Derived Poliovirus (cVDPV) outbreaks: these rare outbreaks occur when a vaccine-related virus is passed from person-to-person, mutating over time and acquiring wild virus transmissibility and neurovirulence characteristics.  Almost all cVDPV outbreaks in recent years have been caused by a type 2 vaccine-derived virus. 

Although wild poliovirus type 2 appears to have been eradicated globally in 1999, vaccine-related type 2 viruses continue to cause the majority of cVDPV outbreaks and many VAPP cases. Therefore, OPV type 2 now carries more risk than benefit and undermines global polio eradication efforts. Thus, tOPV will be replaced with bivalent OPV (bOPV), which will continue to target the remaining polio types 1 and 3. Once these types are eradicated, bOPV will also be withdrawn.


FAQ #1 Why should countries introduce IPV?

Inactivated Polio Vaccine (IPV) Introduction

In May 2012 the World Health Assembly declared the completion of poliovirus eradication to be a programmatic emergency for global public health and called for a comprehensive polio endgame strategy.  In response, the Polio Eradication and Endgame Strategic Plan 2013-2018 was developed.

The planoutlines a comprehensive approach for completing eradication including the elimination of all polio disease (both wild and vaccine-related).

As one of its four major objectives, the plan calls on countries to introduce at least 1 dose of Inactivated Polio Vaccine (IPV) into routine immunization schedules, strengthen routine immunization and withdraw Oral Polio Vaccine (OPV) in a phased manner, starting with type 2-containing OPV. This sheet provides information on the rationale behind this objective.

Why should countries introduce IPV?

Introducing IPV is a key element of the endgame plan and global readiness to manage risks associated with OPV type 2 withdrawal. The endgame plan calls for the introduction of IPV in all OPV-only using countries by the end of 2015. The primary role of IPV will be to maintain immunity against type 2 poliovirus while removing OPV type 2 globally.  More specifically, IPV needs to be introduced for the following reasons:

  • To reduce risks. Once OPV type 2 is withdrawn globally, if no IPV is used, there will be an unprecedented accumulation of children susceptible to type 2 poliovirus.  IPV use will help maintain immunity to type 2.  This will help prevent emergence of type 2 viruses should they be introduced after the type 2 component is removed from OPV.  Thus, a region immunized with IPV would have a lower risk of re-emergence or reintroduction of wild or vaccine-derived type 2 poliovirus.
  • To interrupt transmission in the case of outbreaks. Should monovalent OPV type 2 (mOPV type 2) be needed to control an outbreak, the immunity levels needed to stop transmission will be easier to reach with use of mOPV type 2 in an IPV-vaccinated population compared to use of mOPV type 2 in a completely unvaccinated population.  Thus, introducing IPV now could facilitate future outbreak control.

A WHO Position Paper on polio vaccines published in February 2014 is available online at:


TAG Recommendations on the Polio Eradication and Endgame Strategic Plan 2013-2018


  • TAG expresses concern regarding the reported decline in Polio3 coverage at the national and sub-national levels in the Americas. As such, TAG strongly urges countries to ensure high, homogenous polio coverage to maintain the achievement of polio elimination in the Region.
  • TAG notes the confirmed isolation of WPV1 in Brazil from environmental sampling in the state of Sao Paulo in March 2014 and commends Brazil for its response to this isolation. This finding confirms that the risk of WPV is real for the Region.
  • In light of the newly confirmed risk of WPV importation in the Americas, TAG calls upon PAHO Member States to urgently take action to strengthen AFP active surveillance. The reported decline in the proportion of laboratory specimens of quality collected and timeliness of case investigations jeopardizes the opportune detection of imported WPV (or VDPVs) and rapid deployment of response activities.
  • Due to its high cost and involved methods, expansion of environmental surveillance networks in the Region needs further assessment. TAG recommends that PAHO assess the strengths and weaknesses of existing environmental sampling methods and based on this risk assessment and evaluation of existing methods, PAHO should propose potential options for environmental sampling in selected settings in the Region.
  • PAHO should conduct a risk analysis to identify areas in the Region with a high concentration of WPV importation (and VDPV) risk (i.e. geographic areas with suboptimal polio3 coverage and a large number of international visitors from polio endemic or at risk areas).
  • TAG reiterates the recommendations issued during the extraordinary TAG Meeting on Polio conducted in April 2014:
  • TAG agrees with the renewed efforts towards eradicating polio and the objectives of the polio endgame. These efforts include the ongoing removal of Sabin oral polio vaccine from the routine immunization schedule.
  •  TAG reiterates its previous recommendations, emphasizing:
  • § The importance of achieving and maintaining high and homogenous vaccination coverage rates to reduce risk of importations of WPV and cVDPV, and
  • § The need for continued strengthening of epidemiological AFP surveillance.
  • TAG urges implementation of environmental surveillance towards validating the elimination of cVDPVs and WPV.
  • TAG agrees with the six prerequisites stated by SAGE to switch from tOPV to bOPV.*
  • The countries of the Americas are already in the process of introducing IPV. At the end of 2015, approximately 80% of the birth cohort in the Americas will be covered with IPV. PAHO is providing technical cooperation to the countries on this process.
  • The remaining countries must decide when they will be able to introduce IPV, taking into consideration affordability (price for vaccines and operational costs), current opportunity costs, and sustainability. PAHO should continue working with the countries to help remove barriers for such introduction.
  • When introducing IPV, countries should consider sequential schedules. Ideally, countries should consider two IPV doses followed by two OPV doses. However, if a country is considering only one IPV dose, this should be with the first DTP dose and followed by three OPV doses.
  • Countries should not consider moving directly to an IPV only schedule at this time, unless they meet the criteria previously recommended by TAG and WHO (low risk of transmission and importation, high homogeneous coverage, and good sanitation).

*According to the SAGE’s recommendations, prior to the withdrawal of OPV2 – by replacing tOPV with bOPV in all OPV-using countries, six prerequisites must be in place:

1. Validation of the elimination of persistent cVDPV type 2 and confirmation of WPV2 eradication;
2. A mOPV type 2 stockpile and response capacity;
3. Surveillance capacity and an international notification requirement for all Sabin, Sabin-like, and cVDPV type 2 viruses;
4. Sufficient bOPV products for all OPV-using countries;
5. Affordable IPV option(s) for all OPV-using countries;
6. Phase II bio-containment of all cVDPVs type 2 and WPV.

Source: XXII TAG Meeting Washington DC, 2014 - Final Report, pp.13


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