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Indian Pediatr 2012;49: 787 |
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Inactivated Poliovirus Vaccine: The Fog of
Uncertainty is Lifting!
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T Jacob John
Thekkekara, 439 Civil Supplies Godown Lane,
Kamalakshipuram, Vellore, TN 632 002.
Email: [email protected]
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I ndia achieved zero
transmission of wild polioviruses (WPVs) in 2011. On 25 February, 2012,
the World Health Organization (WHO) removed India from the list of
WPV-endemic countries. Formal certification of eradication requires
three years without WPVs, expected in the first quarter of 2014. Then we
have to advance to the second phase of polio eradi-cation, for
eliminating vaccine polioviruses (VPVs) [1].
Albert Sabin derived VPVs by attenuating WPVs. Two
major phenotypic changes were brought about by genetic variations: loss
of neurovirulence and reduction in ‘force of infection’. Force of
infection determines the efficiency of transmission between hosts: VPVs
are less efficient in transmission than WPVs. Polioviruses, with single
stranded positive sense RNA genome, acquire point mutations during
replication. As a result, VPVs tend to revert genetically during cycles
of virus replication. In serial replication in humans, VPVs de-attenuate
and become ‘vaccine-derived polioviruses’ (VDPVs) [2]. If all children
are fully vaccinated with OPV, VDPVs will not emerge but the price to
pay will be the occasional vaccine-associated paralytic polio (VAPP).
So, OPV has to be withdrawn, when the stray VDPVs will circulate
unchecked among children, become ‘circulating VDPVs’ (cVDPVs) and
replace the eradicated WPVs. The emergence of cVDPVs should therefore be
preempted at all costs [1]. We already have the necessary tool of
intervention, the inactivated poliovirus vaccine (IPV) developed by
Jonas Salk.
Now the contours of eradication phase 2 are clear:
introduce IPV, achieve high coverage, discontinue OPV and maintain
clinical and virological surveillance [1]. These steps will have to be
orchestrated globally in order to conclude polio eradication. WHO is
planning to discontinue VPVs in stages, starting with withdrawal type 2
by switching from trivalent to bivalent OPV (bOPV, containing types 1
and 3), since WPV type 2 was eradicated in 1999. In preparation for this
shift, IPV needs to be introduced universally. Where schedule-based
vaccination will not achieve high coverage, to begin with IPV may have
to be given in campaigns. After WPV 1 and 3 are eradicated, bOPV will
also be withdrawn.
Many countries currently use IPV-containing
pentavalent vaccine with DPT with acellular pertussis (aP) component and
Haemophilus influenza b (Hib) conjugate vaccine or hexavalent
vaccine containing hepatitis B vaccine (HB) also. Hexavalent is ideal
for India since we have HB and Hib in our Universal Immunisation
Programme (UIP). If hexavalent with wP can be made, that will be even
better.
Investigators from Delhi and Vellore have conducted
clinical trials of a pentavalent vaccine manufactured in France [3, 4].
In primary series in UIP schedule (6, 10, 14 weeks of age), immune
responses were excellent to all components, quite similar to those
obtained in France using a 2, 3, 4 months schedule [3]. In this issue,
they report on a booster dose given in the second year of life; the
seroresponses were excellent – achieving very high antibody levels to
each antigen [4]. Taken together, they show that IPV-containing
combination vaccines can immunize well when given according to our UIP
schedule for DPT — primary series at 6, 10, 14 weeks and a booster in
the second year of life. We now await the revision of national policy
for the introduction of IPV in UIP.
Competing interests: None stated; Funding:
Nil.
References
1. John TJ, Vashishtha VM. Eradication of vaccine
polioviruses: why when and how? Indian J Med Res. 2009;130:491-4.
2. Kew O, Morris-Glasgow V, Landaverde M, Burns C,
Shah J, Garib Z, et al. Outbreak of poliomyelitis in Hispaniola
associated with circulating type 1 vaccine-derived poliovirus. Science.
2002;296:356-9.
3. Dutta AK, Varghese VP, Pemde HK, Mathew LG, Ortiz
E. Immunogenicity and safety of a pentavalent diphtheria, tetanus,
acellular pertussis, inactivated poliovirus, Haemophilus influenzae
type b conjugate combination vaccine (Pentaxim) with hepatitis B
vaccine. Indian Pediatr. 2009;46:975-82.
4. Dutta AK, Varghese VP, Pemde HK, Mathew LG, Ortiz
E. Immunogenicity and safety of a DTaP-IPV/PRP~T vaccine booster dose
during the second year of life in Indian children primed with the same
vaccine. Indian Pediatr. 2012; 49:793-8.
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