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?
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.
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.
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
Polio Vaccine (IPV) Introduction
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.
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.
should countries introduce IPV?
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.
Position Paper on polio vaccines published in February 2014 is available online
- 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
- 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;
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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