How smallpox showed the way

How smallpox showed the way T en years have passed since a WHO Commis-sion declared that for the first time in history, a disease - smallpox - had been eradicated from the globe. Small- pox hospitals are no longer needed and its vaccination every.vhere has stopped. The annual savings are at least US $1,000 million, more than three times the cost of the entire programme. Given these extraordinary benefits, it was logical for scientists to ask whether other diseases might be candidates for eradication. After lengthy discussions, they decided that poliomyelitis was the best prospect. Accordingly, the World Health Assembly in 1988 agreed on a global polio eradication campaign to be com- pleted by the year 2000. The two diseases, poliomyelitis and smallpox, differ in many ways, as do the vaccines for preventing them and strategies for their eradication. Know- ing what we do about the problems in eradicating smallpox, what can we say about the prospects for getting rid of polio? In some respects, polio eradi- cation should be easier, but there are far more difficult technical problems, especially in the detection and diag- nosis of cases and in the quality of vaccine available. Research is urgently required to address these aspects. On the positive side, the infrastruc- ture of transport, communications and health services has improved greatly over the past two decades in virtually all countries. There are far larger numbers of trained health staff; radio, telephone and even television are found in areas where none existed 20 years ago; and air and road transport leave few populated areas on the globe which are truly inaccessible. Admittedly, there are larger popu- lations and a greater movement of people who may spread disease, but these are not major problems. Most encouraging is the already demonstrated political commitment on Franklin D. Roosevelt, 32nd President of the United States, had polio as a young man and remained paralysed for the rest of his life. He lent powerful support to the fight against polio in his country. W ORLD HEALTH. December 1989 by Donald A. Henderson the part of governments throughout the world, as well as international assistance agencies, to assign a high priority and resources to the effort. I sense a greater commitment than there was to smallpox eradication when it began. This may appear puzzling because smallpox, notably in Asia and Africa, caused many times more cases and deaths than does poliomyelitis. However, smallpox patients who survived returned to normal health. Most poliomyelitis victims, in contrast, are sentenced to lifelong paralysis and dependency. In the poorer countries, most survive as beggars. Poliomyelitis is thus a more constantly visible disease and, not surprisingly, is greatly feared. Or Donald A. Henderson led the WHO successful battle ag ainst smallpox from 1966 to 1977. He is now Dean of the School o f Hyg iene and Public Health at the Johns Hopkins University, Baltimore, Maryland, USA The first national efforts to defeat poliomyelitis began in the United States during the 1930s. They were encouraged by President Franklin D. Roosevelt, who had been crippled by polio as a young man and thereafter was confined to a wheelchair. With his WHO/ US National Foundation for Infantile Paralysis support, the National Foundation for Infantile Paralysis (as polio was then called) raised large sums of money for prevention research and treatment. Meanwhile, the number of cases each year rose steadily until, during the early 1950s, 30,000 to 50,000 cases were being reported annually in the USA alone. During the summer polio season, theatres, swimming pools and other facilities were frequently closed to prevent children from gathering and spreading infection. The discovery and introduction of an inactivated (Salk) vaccine in 1955 and, soon afterwards, of a live oral (Sabin) vaccine were landmark events. In little more than a decade, polio cases in the industrial- ised countries dropped from more than 75,000 per year to fewer than 1,000. Until the 1970s, many scientists believed that paralysis due to polio- myelitis was primarily a problem of the industrialised countries. They believed that children in the developing coun- tries were infected early in life and did not experience paralysis. When rehabi- litation centres developed, however, it soon was apparent that polio victims accounted for most of their patients. Special surveys to detect lameness in children quickly revealed that it was an important problem in all developing countries. Thus, when the Expanded 19 How smallpox showed the way Programme on Immunization began in 1974, polio vaccine was one of the vaccines to be included. The effects of polio itself have served to foster a political commitment to the programme so that, today, international and national authorities alike know that global polio eradi- cation can be accomplished. They have confidence that national health se!Vices can be effectively mobilised, even in the least developed parts of the \\IOrld.. They have also seen that adding resources for the polio cam- paign strengthens other community- based ~es, such as those for immunization, family planning, diar- rhoea~: disease and vitamin A defi- ciency. Today, many agencies which did not oontribute to smallpox eradi- cation are providing important support rox the polio campaign. These include UNICEF, the Inter American Develop- ment Bank and many bilateral agen- cies. Rotary International Foundation, In addition to providing volunteer support, has pledged to raise US$125 mi!Uion, an unprecedented 1ype of ooRaboraoon b) pnvate citizens. In fact, Rotary ~ alieady raised more than ~this sum! The better m.&asbuctule and more ~ favourable response: to polio eradi- cation is counterbalanced by two iro)OOriant problems which make the task of era.dl.'caoon more diHkult than was the case with smallpox.. The first pertains to difficulties in detecting the presen~ of PQlio virus in an area and Knmm in the 1950s as "infantile paraly- ~ •• p€100 was a unWersaJ problem. But few people tbes applf!dated its cata- stropbk: elleds in the Third World. Right Quite modest labocatories. like this ose in Yemen. will help to bring .,. polio emdkation. in oontaln~Jil9 its spread. - the impor- tant SUNeill~containment strategy of ~ sma11}oox programme. The ~ probl~ is that PQlio vaccine is ress efifkadous and ress ~t-stabte than was sm.~lPQX vaccine,. thus makiJilg ~tt more diffirult and oostly; to oondudt the l~scale vocclnati.on. pr~ that are called for. ··- z-..ls esse.,.. l'tt is mt!ical! in an eradication cam- paign to know where cases are ~ng: and h.Qw ~ vints is spread- ing. in m~ to altocate r~wces opt!imall~ and to make n~ cltamges in strateg}'. The characteristic sm.allpox:. ~. was ~clbm. oon.fuSJed wttm aiilSll <fltm dis:e~,. so 1ilha.tt laoomr ~ studtes to oonmm the di~ were u.n~ u.nmM the campaign was dfrawiil1l9 to an end. Eadh smallJ!l()x ~wtt foo,ncl! oo~M oo roorated and al!li OOiiltads v~nat.~. thus ex;dng a bam~ against ~ spread ~e.n ~ as fe.w as hali Ci)i th0 roopt.ciai!i<?ln was; '<lacciinat~.- These wer~ tth~ er~ oft~ 1m{OOl1tantt smv~l~ OOl!l:tain~tt sWat~. ~ ~ootc <d~OO: aoo OOl'ilt~n ~ ~ Cflfr polio Wl!l.s as l'~ as w~ did smallpox. Of those infected with poli<>Wus, fe~Ner than 1 in 100 child- ren develop parnlysis. The others have no symptoms. So a patient paralysed with poliomyelitis represents only the tip of the iceberg of infection in the oommunity. If one case is discovered, it must oo assumed that there are many other infected chil.dren. laboratory studies would be time-consuming and imprii.lCOC.abfe as they \\IOuld require examining hundfeds, if not thousands, of contacts. So the simple technique of oontad-tracing of cases and contain- ment of outbreaks, which proved so effecmte m smallpox eradication, is not feasible for polio. tn. addition there are some paralYtic illnesses which mimic the dis.ease but are not caused by' polio virus.. To be certain that a paralytic Ufness is caused' by; polio virus, the virus m.u.st be isolated from a stool specimen. This requires moderately sopnislicated laboratories which can ncl on~ isolate the virus but can ~lrrie whether ~t is a vaccine virus m· a St>rcalf~ ''wild''' virus. The countries of the Americas, which began a hemisphere-wide cam- paign in 1985, are using new strategies for polio surveillance and containment. So far, they appear to be working. Each health centre and hospital is required to report promptly every case of flaccid paralysis in children less than 15 years old. An epidemiologist visits each case within 48 hours and collects a stool specimen. If there is no other apparent diagnosis, the case is called a "probable" polio case and intensive vaccination is immediately performed throughout that community. Specially equipped laboratories require bet\.veen 30 and 60 days to examine each specimen and confirm the diagnosis. During 1988, more than 6,000 stool W ORLD HEALTH, December 1989 I. specimens were examined - a very large task indeed. Progress in the Americas is encou- raging. During 1988, fewer than 50 wild polio viruses were isolated and polio cases were found in less than two per cent of all counties or districts. Even fewer cases are being discovered in 1989. Epidemiological evidence so far suggests that the wild polio viruses, like smallpox, do not spread readily over great distances and that the principal reservoirs for transmission are the more. densely populated and lower socio-economic areas. It is here that special house-to-house vaccination campaigns are now being conducted. The second major problem in the polio campaign is the vaccine. The freeze-dried smallpox vaccine was very stable even under tropical conditions; a successful vaccination always caused a pustule to form on the arm and subsequently a scar. Moreover, a single vaccination conferred nearly complete protection for at least five to ten years. The success of the vaccination pro- gramme and the immune status of a population could therefore be readily determined by surveying scars and/ or pustular responses following vaccination. For a number of reasons, including cost, the oral polio vaccine is being WOR LD HEALT H. December 1989 How smallpox showed the way used. It has the advantages of being inexpensive and easily administered even by lay persons - a few drops being placed in the mouth. The vac- cine virus, a greatly weakened polio virus strain, grows in the intestine and causes protective antibodies to be produced. It can spread to contacts of the vaccinee and immunize them as well. However, the vaccine is rapidly destroyed by high temperatures, so refrigerators and ice-boxes are needed to transport it into the field. High levels of protection require as many as four or five doses but, even then, other viruses growing in the intestinal tract may prevent its growth and limit the protection that children need. Finally, there is no simple way to determine whether or not a child is protected. If, for example, the vaccine has been destroyed by heat,. it will appear perfectly normal but will be of no more value than a few drops of water. Despite the drawbacks of the vac- cine, it can serve to stop the spread of polio. In the USA, for example, wild virus transmission stopped in the early Detection and diagnosis of polio cases calls for special skills on the part of health workers. 1970s at a time when only about 70 per cent of pre-school-age children were vaccinated. Similarly, in South America, intensive one to two day vaccination campaigns with good coverage have served to reduce polio incidence dramatically, and in some countries to stop transmission within a matter of a few years. Heat-stable vaccine The prospects for polio eradication would be greatly enhanced if we had a more heat-stable vaccine producing higher levels of immunity with fewer doses, and if we had simpler, more rapid laboratory diagnostic tests. Scientists now believe that these prob- lems could be solved comparatively quickly, but additional funds for research will be necessary to do so. The achievement of global polio eradication by the year 2000 is by no means a certainty. It will require a high level of sustained commitment and resources, and close collaboration between politicians, public health field staff and laboratory workers. Strategies will need to be continually adapted and modified as more is learned. Yet the success of polio eradication could well be the most significant step toward guaranteeing a high quality of life for all children. • 21