Rev. Med. Virol. 2011; 21: 259–261.Published online in Wiley Online Library

(wileyonlinelibrary.com)DOI: 10.1002/rmv.709

E D I T O R I A L

Elimination or eradof immunisation

Reviews in Medical Virology

Copyright © 201

ication of viruses by means

`Then you should say what you mean,’ the MarchHare went on.`I do,’ Alice hastily replied; `at least—at least I

mean what I say—that’s the same thing, youknow.’Lewis Carroll. Alice’s Adventures in Wonderland.

The elimination of measles from parts of theworld and potential eradication of poliovirus hasgenerated some interesting discussion [1–4]. Wherebetter to start than with a definition of these twoterms which are often confused [5]. The term elimi-nation is used when endemic transmission of agiven virus has been extinguished at a regional orgeographical level. An excellent example wouldbe elimination of rubella from the Americas whoselast endemic case was in 2009. Regions with elimi-nation remain at risk of importation of cases unlessevery part of the world achieves elimination.Global eradication is then declared once the world-wide incidence of infection has been permanentlyreduced to zero. A formal declaration of eradica-tion requires that quality controls specific for eachvirus have been met, such as monitoring for acuteflaccid paralysis and collecting stool samples inthe case of polio.When WHO launched the global polio eradica-

tion initiative (GPEI) in 1988, approximately350 000 children were paralysed annually in 125 en-demic countries. By October 1999, wild type polio-virus 2 (WPV2) had been eradicated. By 2006, onlyfour countries (Afghanistan, India, Nigeria andPakistan) had never interrupted indigenous circu-lation of wild type polioviruses. However, between2002 and 2006, genomic sequencing revealed thatNigeria was the source of WPV1 for 20 countriesin Africa and Asia which had previously been poliofree, whereas India was the source of WPV1 forthree African countries [6]. By 2008, many of theseoutbreaks were coming under control when multi-ple further importations into African and Asiancountries took place from Nigeria and India [7]. In2010, the WHO European Region, which had been

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certified to be free of polio in 2002, was involvedwhen Tajikistan had an outbreak of WPV1 whichoriginated from India [8]. Overall, 39 countrieswhich had previously been free of polio becameinfected, illustrating that their routine levels ofimmunisation were clearly below those requiredto stop indigenous transmission. Intensive effortshave managed to row back from these relapses us-ing, for example, 309 supplementary immunisationactivities which delivered 2.2 billion doses of oralpolio vaccine to approximately 400 million people,mostly children [7]. These ongoing efforts have beenhelped by the availability of bivalent oral polio vac-cine (40% of the 2.2 billion doses mentioned earlier)which is safe, effective and more potent [9] becausepossible interference fromWPV2 (no longer neededbecause of its eradication) has been removed fromthe original trivalent vaccine. Administration ofthis bivalent vaccine instead of monovalent oralpolio 1 has also helped to bring the global numberof cases of WPV3 to its lowest ever level [7]. Thiscontributed to India reporting its best ever controlof wild type polio in 2010. Although extensiveinvestment will still be required to contain wildtype polioviruses within the boundaries of the fourcountries which have never been able to eliminatethem, it seems possible that one of the key mile-stones in the 2010–2012 GPEI strategic plan [10] ofinterrupting transmission of wild type poliovirusin at least two of these four reservoir countries bythe end of 2011 might be achievable. Although somecommentators are disappointed that polio has not yetbeen eradicated, they must be reminded that thesubstantial achievements to date have come whilemany of the populations affected are being disruptedby war, civil unrest or competing public healthemergencies such as the 2010 floods in Pakistan.

Having eradicated two human viruses from theplanet (smallpox; WPV2), five out of six WHORegions are now targeting measles virus for elimi-nation as a staging post towards a potential dateof 2020 for eradication [11,12]. The health benefitsto be gained from this are clear because measles is

260 Editorial

a major cause of mortality, and global deaths havealready been reduced by 78% between 2000 and2008. However, measles virus will be a formidableadversary because it is so highly contagious. Witha basic reproductive number of 15, 93% of the pop-ulation need to be protected in order to interrupttransmission, compared with the correspondingfigures of six and 83% for polio [13]. Nevertheless,the solid lifelong immunity and single serotype ofmeasles could be its Achilles’ heel, because it needsserial access to susceptibles in order to survive.Measles has been eliminated from the Americas,with the last indigenous case reported in 2002. Thishas led to a bold initiative to target measles foreradication [11,12], but this has not been met withacclamation. Commentators have questionedwhether measles should be accepted as a target be-fore all three serotypes of poliovirus have beeneradicated [2]. Furthermore, they suggested thateradication should only be attempted once routineimmunisation coverage has been proven to be suf-ficient in all six WHO regions and emphasised thatexcellent results at regional level could still hidesignificant variability at national or subnationallevel, sufficient to sustain chains of transmission[2]. In response, others emphasise the advantagesof using sequential campaigns to retain essentialhuman and physical infrastructure [4,14]. Thus,equipment able to sustain a cold chain and trainedhealthcare workers can be deployed to control morethan one virus. This plurality is important as the costper case accelerates as a region approaches elimina-tion. Indeed, such infrastructure has also deliveredinsecticide treated nets, deworming tablets and vita-min A to the world’s poorest children, thereby sus-taining support from local communities whootherwise might question the WHO focus on thenow rare condition of polio when they experiencemore pressing needs on a daily basis [14].

Copyright © 2011 John Wiley & Sons, Ltd.

Amajor advantage of eradication is its cost effec-tiveness; it is equivalent to a capital payment whichsaves many years of future revenue expenditure.Despite the delay in achieving eradication of polioand the increased costs of GPEI, the programmeremains highly cost-effective with aggregated netbenefits of tens of billions of dollars [15]. As I writethis editorial sitting in my garden at home, our elec-tricity supplier is installing solar panels as our con-tribution to help control global warming. Thesalesman was delighted to tell me that the paybackperiod was only 9 years, but crestfallen when I toldhim that was very poor when compared withsmallpox, whose eradication by WHO paid backthe funds given by the major contributor (theUSA) within 1month [16]. In these financiallystraitened times, we should not miss the opportu-nity to emphasise how cost-effective (as well asmedically beneficial) investment in virology canbe. To be fair, the full financial benefits of eradica-tion will only be realised if it is possible to stopimmunisation and the costs associated with it. Thismay be possible scientifically and medically, yetmay not be achieved politically because of anotherfactor; fear of bioterrorism. Thus, some countriesmight choose to continue immunising their popula-tions against an eradicated virus for strategic rea-sons even if, like polio, the virus would make apoor bioweapon because of the large excess ofasymptomatic cases. If countries wish to do this,perhaps the costs should be charged to the militarybudget (as would be the case for selective immuni-sation of troops) so that health services can trulyclaim to have a cost effective intervention whenviewed from their perspective of providing protec-tion against natural health hazards.

P. D. Griffiths

REFERENCES

1. Heymann DL, Fine PE, Griffiths UK, Hall

AJ. Measles eradication - authors’ reply.

Lancet 2011; 377: 809–810.

2. Heymann DL, Fine PE, Griffiths UK, Hall

AJ, Mounier-Jack S. Measles eradication: past

is prologue. Lancet 2010; 376: 1719–1720.

3. Durrheim DN, Bashour H. Measles eradica-

tion. Lancet 2011; 377: 808–810.

4. Andrus JK, de Quadros CA. Measles eradi-

cation. Lancet 2011; 377: 809–810.

5. Dowdle WR. The principles of disease

elimination and eradication. Bulletin of the

World Health Organization 1998; 76(Suppl

2): 22–25.

6. MMWR. Wild poliovirus type 1 and type 3

importations--15 countries, Africa, 2008–2009.

MMWR Morbidity and Mortality Weekly

Report 2009; 58: 357–362.

7. MMWR. Progress toward interruption of

wild poliovirus transmission--worldwide,

R

January 2010-March 2011. MMWR Morbid-

ity and Mortality Weekly Report 2011; 60:

582–586.

8. MMWR. Outbreaks following wild poliovi-

rus importations --- Europe, Africa, and

Asia, January 2009-September 2010.

MMWR Morbidity and Mortality Weekly Re-

port 2010; 59: 1393–1399.

9. Sutter RW, John TJ, Jain H, Agarkhedkar S,

RamananPV, Verma H, et al. Immunogenicity

ev. Med. Virol. 2011; 21: 259–261.DOI: 10.1002/rmv

261Editorial

of bivalent types 1 and 3 oral poliovirus

vaccine: a randomised, double-blind, con-

trolled trial. Lancet 2010; 376: 1682–1688.

10. Donaldson L. Report of the Independent

Monitoring Board of the Global Polio

Eradication Initaitve. 2011.

11. Levin A, Burgess C, Garrison LP, Jr., Bauch

C, Babigumira J, Simons E, et al. Global

eradication of measles: an epidemio-

logic and economic evaluation. Journal

Copyright © 2011 John Wiley & Son

of Infectious Diseases 2011; 204(Suppl 1):

S98-106.

12. Moss WJ, Strebel P. Biological feasibility

of measles eradication. Journal of Infectious

Diseases 2011; 204(Suppl 1): S47-S53.

13. McLean AR. Mathematical Modelling of

the Immunisation of Populations. Reviews

in Medical Virology 1992; 2: 141–152.

14. Christie A, Gay A. Measles eradication.

Lancet 2011; 377: 807–808.

s, Ltd. R

15. Duintjer Tebbens RJ, Pallansch MA, Cochi

SL, Wassilak SG, Linkins J, Sutter RW,

et al. Economic analysis of the global polio

eradication initiative. Vaccine 2010; 29:

334–343.

16. Fenner F, Henderson D, Arita I, Jezek Z,

Lidnyi I. Smallpox and its Eradication.

World Health Organisation; 1988.

ev. Med. Virol. 2011; 21: 259–261.DOI: 10.1002/rmv