E-DRUG: NEJM on poliovirus vaccine in Nigeria (3)
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Hi again,
I got confused and sent you the link and abstract of the study done in
EGYPT- which is worth looking at anyway.
However, there is indeed also a study on polio immunization in Nigeria
(abstract below) and an editorial on monovalent on oral polio vaccines
in the same NEJM issue (also copied below), see
http://content.nejm.org/current.shtml
Valeria
359:1666-1674 October 16, 2008 Number 16
Effectiveness of Immunization against Paralytic Poliomyelitis in
Nigeria
Helen E. Jenkins, M.Sc., R. Bruce Aylward, M.D., Alex Gasasira, M.B.,
Ch.B., Christl A. Donnelly, Sc.D., Emmanuel A. Abanida, M.P.H., Titi
Koleosho-Adelekan, Ph.D., and Nicholas C. Grassly, D.Phil.
ABSTRACT
Background: The number of cases of paralytic poliomyelitis has declined
in Nigeria since the introduction of newly licensed monovalent oral
poliovirus vaccines and new techniques of vaccine delivery.
Understanding the relative contribution of these vaccines and the
improved coverage to the decline in incident cases is essential for
future planning.
Methods: We estimated the field efficacies of monovalent type 1 oral
poliovirus vaccine and trivalent oral poliovirus vaccine, using the
reported number of doses received by people with poliomyelitis and by
matched controls as identified in Nigeria's national surveillance
database, in which 27,379 cases of acute flaccid paralysis were recorded
between 2001 and 2007. Our estimates of vaccine coverage and
vaccine-induced immunity were based on the number of doses received by
children listed in the database who had paralysis that was not caused by
poliovirus.
Results: The estimated efficacies per dose of monovalent type 1 oral
poliovirus vaccine and trivalent oral poliovirus vaccine against type 1
paralytic poliomyelitis were 67% (95% confidence interval [CI], 39 to
82) and 16% (95% CI, 10 to 21), respectively, and the estimated efficacy
per dose of trivalent oral poliovirus vaccine against type 3 paralytic
poliomyelitis was 18% (95% CI, 9 to 26). In the northwestern region of
Nigeria, which reported the majority of cases during the study period,
coverage with at least one dose of vaccine increased from 59 to 78%.
Between 2005 and 2007, vaccine-induced immunity levels among children
under the age of 5 years more than doubled, to 56%.
Conclusions: The higher efficacy of monovalent type 1 oral poliovirus
vaccine (four times as effective as trivalent oral poliovirus vaccine)
and the moderate gains in coverage dramatically increased
vaccine-induced immunity against serotype 1 in northern Nigeria. Further
increases in coverage in Nigerian states with infected populations are
required to achieve the levels of vaccine-induced immunity associated
with the sustained elimination achieved in other parts of the country.
Source Information
From the Medical Research Council (MRC) Centre for Outbreak Analysis
and Modeling, Department of Infectious Disease Epidemiology, Faculty of
Medicine, Imperial College London, London (H.E.J., C.A.D., N.C.G.); the
Global Polio Eradication Initiative, World Health Organization (WHO),
Geneva (R.B.A.); and WHO-Nigeria (A.G.) and the National Primary Health
Care Development Agency (E.A.A., T.K.-A.) - both in Abuja, Nigeria.
Address reprint requests to Ms. Jenkins at MRC Centre for Outbreak
Analysis and Modeling, Department of Infectious Disease Epidemiology,
Faculty of Medicine, St. Mary's Campus, Imperial College London, Norfolk
Pl., London W2 1PG, United Kingdom, or at h.jenkins@imperial.ac.uk.
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359:1666-1674 October 16, 2008 Number 16
Monovalent Oral Poliovirus Vaccines — A Good Tool but Not a Total
Solution
Ellie Ehrenfeld, Ph.D., and Konstantin Chumakov, Ph.D.
The polio eradication campaign initiated in 1988 by the World Health
Organization (WHO) led to an impressive decline in cases of paralytic
poliomyelitis around the world.
The eradication strategy involved highly
organized mass immunization campaigns, relying solely on the trivalent
oral polio vaccine developed by Albert Sabin and licensed in the United
States in 1963. Monovalent versions of oral polio vaccine had been
licensed earlier but were abandoned in favor of the trivalent
combination oral polio vaccine to simplify immunization schedules.
Efficacy was not considered to be a significant issue, and differences
between monovalent and trivalent vaccines were never formally assessed.
At the turn of the century, global transmission of wild-type poliovirus
type 2, one of the three serotypes of the virus, had been successfully
interrupted. The elimination of this serotype represented a milestone
for the eradication initiative; however, further progress toward
eradication began to falter. Even today, circulation of endemic virus
continues in several geographic pockets (northern Nigeria, northern
India, and the Pakistan/Afghanistan border) that continue to be a
source of reintroduction of wild-type virus into countries where
transmission had previously been stopped. Obstacles to eradication have
included incomplete vaccination coverage and inadequate efficacy of oral
poliovirus vaccine. In some densely populated areas of India, it
appeared that trivalent oral poliovirus vaccine was not sufficiently
immunogenic to eliminate the circulation of wild-type virus, especially
in the context of extraordinarily high birth rates, poverty, and poor
sanitation. New vaccine products were sought to achieve the final goal
of eradication. A few previous trials of monovalent oral poliovirus
vaccine had suggested that monovalent type 1 oral poliovirus vaccine was
two to three times as immunogenic as trivalent oral poliovirus vaccine1
because it eliminated interference from the other two poliovirus
serotypes. The Global Polio Eradication Initiative issued an urgent call
for the development of a monovalent product to boost immunogenicity, and
in 2005, a new monovalent type 1 oral poliovirus vaccine with higher
potency was quickly licensed and put to use.
In this issue of the Journal, two clinical studies are reported that
provide direct comparisons of the efficacies of the new monovalent type
1 oral poliovirus vaccine and the conventional trivalent oral poliovirus
vaccine. One study2 of vaccine-induced protection was conducted in
northern Nigeria, where a temporary suspension of all poliovirus
immunization in one state in 2003 contributed to a national epidemic of
poliomyelitis and reinfection in more than 20 countries that had been
poliomyelitis-free. Even after the reversal of the suspension, vaccine
coverage has remained low in northern Nigeria. According to field
studies of the reported number of doses received by case patients and
matched controls, the estimated efficacy of monovalent type 1 oral
poliovirus vaccine per dose against type 1 poliomyelitis was four times
as great as that of the trivalent oral poliovirus vaccine. At the same
time, a new strategy of vaccine delivery, in which oral poliovirus
vaccine was offered together with a range of additional pediatric
vaccinations and other health services, resulted in moderate gains in
coverage. Together, these two interventions markedly increased
vaccine-induced immunity in the region.
The other study, designed to directly measure immunogenicity, took
place in Egypt.3 Seroconversion rates were determined after
administration of a dose of either vaccine at birth, and virus excretion
was measured after subsequent challenge with monovalent type 1 oral
poliovirus vaccine. The results showed that when given at birth,
monovalent type 1 oral poliovirus vaccine was more effective at inducing
production of humoral antibodies and at reducing virus excretion after
challenge. The relative contributions of increased vaccine potency and
lack of interference by the other two serotypes to the increase in
efficacy is not known.
Both of these studies confirm the potential usefulness of supplemental
doses of monovalent oral poliovirus vaccine as an effective tool for
interrupting persistent chains of wild-type virus transmission, as
previously shown in northern India,4 and thereby accelerating the path
to eradication. The authors of the Nigerian study emphasize that in some
regions, considerable improvements in vaccine coverage will still be
required to eliminate the current gaps in immunity that impede
eradication, despite the boost provided by monovalent oral poliovirus
vaccine supplements. Although reducing vaccine failure does not
compensate for failure to vaccinate, the newly formulated monovalent
type 1 oral poliovirus vaccine and, by extrapolation, monovalent type 3
oral poliovirus vaccine are welcome additions to the toolbox we are
relying on to eliminate transmission of wild-type polioviruses.
The damper on the fire of enthusiasm, however, is the growing
realization that complete eradication of poliomyelitis must include
eventual eradication of the live oral poliovirus vaccine itself, whether
trivalent or monovalent.5 Documentation of the genetic instability of
the oral poliovirus vaccine, emergence of circulating neurovirulent
vaccine-derived polioviruses, long-term excretion of virus by
immunodeficient vaccinees, and promiscuous recombination between vaccine
polioviruses and nonpoliovirus enteroviruses have all been presented and
discussed in the recent literature.6 Use of oral poliovirus vaccine must
eventually stop; this step has been part of the eradication plan from
the beginning. Unfortunately, poliovirus will not go away after
circulation of wild-type virus is halted, and a high level of immunity
in the global population must be maintained — and not just in
high-income countries that have already switched to the safer but more
expensive inactivated poliovirus vaccine.7
Although accelerating the final steps to eradication of wild-type virus
is unquestionably desirable, we must be prepared for the posteradication
phase with a safe, affordable inactivated poliovirus vaccine that can be
incorporated into a universal, routine pediatric immunization program.
Inactivated poliovirus vaccine could also play a role in facilitating
interruption of the transmission of wild-type virus in developing
countries. Inclusion of an additional group in the Egyptian study might
have been used to assess the effectiveness of inactivated poliovirus
vaccine as a tool for interrupting virus transmission; preliminary
studies conducted last year in Cuba showed that inactivated poliovirus
vaccine effectively reduced transmission of the virus after an oral
poliovirus vaccine challenge in that setting.8 Such data would help
prepare for the ultimate and long-term incorporation of an inactivated
poliovirus vaccine into the WHO Expanded Program on Immunization.
Supported in part by the intramural research programs of the National
Institute of Allergy and Infectious Diseases, the Center for Biologics
Evaluation and Research, the Food and Drug Administration, and the
Department of Health and Human Services.
No potential conflict of interest relevant to this article was
reported.
References
1 Caceres VM, Sutter RW. Sabin monovalent oral polio vaccines: review of
past experiences and their potential use after polio eradication. Clin
Infect Dis 2001;33:531-541.
2 Jenkins HE, Aylward RB, Gasasira A, et al. Effectiveness of
immunization against paralytic poliomyelitis in Nigeria. N Engl J Med
2008;359:1666-1674. [Free Full Text]
3 El-Sayed N, El-Gamal Y, Abbassy A-A, et al. Monovalent type 1 oral
poliovirus vaccine in newborns. N Engl J Med 2008;359:1655-1665. [Free
Full Text]
4 Grassly NC, Wenger J, Durrani S, et al. Protective efficacy of a
monovalent oral type 1 poliovirus vaccine: a case-control study. Lancet
2007;369:1356-1362. [Erratum, Lancet 2007;369:1790.]
5 Dowdle WR, De Gourville E, Kew OM, Pallansch MA, Wood DJ. Polio
eradication: the OPV paradox. Rev Med Virol 2003;13:277-291.
6 Ehrenfeld E, Glass RI, Agol VI, et al. Immunisation against
poliomyelitis: moving forward. Lancet 2008;371:1385-1387.
7 Chumakov K, Ehrenfeld E, Wimmer E, Agol VI. Vaccination against polio
should not be stopped. Nat Rev Microbiol 2007;5:952-958.
8 The Cuba IPV Study Collaborative Group. Randomized, placebo-controlled
trial of inactivated poliovirus vaccine in Cuba. N Engl J Med
2007;356:1536-1544. [Free Full Text]