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Prevention of SmallpoxSMALLPOX is continuing in South Wales; and, though

deaths from this disease are few, they are particularlydistressing because they are felt to be preventable.Prevention, however, is a complex task, dependingalike on screening of immigrants, prompt detectionof cases and of contacts, and a high rate of immunity inthe indigenous population. Screening of those whoreach this country, however ardently practised, cannotbe assuredly effective : as Dr. S. C. ROGERS points outin his letter on p. 587, an international certificate ofvaccination may not mean what it says; and, even if itdoes, the holder may not be immunised. Our public-health service being highly developed, most cases

arriving in this country are detected, and contacts

traced, with reasonable dispatch. It is in the third

requirement-routine vaccination-that our defence isweakest.

Primary vaccination is best, and most safely, under-taken below the age of 1 year: the Ministry of Healthsuggests that for a thriving infant the age of choice isprobably 4 months. 1 Yet, though the primary-vaccination rate of infants under 1 year of age has

latterly been rising, in 1959-60 it was still only 41.3%.2Last month it was reported that, of 21 recent cases ofsmallpox in this country, only 13 had been vaccinatedat any time; of these 13, only 9 had been vaccinated inthe past seven years-and these 9 included 4 vaccinatedafter contact with smallpox.3 One way to raise the

primary-vaccination rate might be to reintroduce anelement of compulsion as regards infants; but a PrivateMember’s Bill which would have had this effect hasbeen rejected by the House of Commons.4 Mostworkers would probably agree that the House was

right. The legal compulsion of the Vaccination Actswas never effective; and indeed in many areas thevaccination-rate rose after its repeal under the NationalHealth Service. Furthermore, any attempt at com-

pulsion might reasonably be regarded as unjustifiedinterference with personal freedom, particularly becausevaccination is itself not devoid of risk. In England andWales in 1960, 2 patients died of generalised vaccinia,and 8 cases of postvaccinial encephalomyelitis (ofwhich apparently 5 proved fatal) were reported.2 Theseare disturbing figures-but by no means as disturb-

ing as the likely total of deaths from smallpox if thepopulation were wholly unvaccinated. The sensiblecourse seems to be to pursue voluntary vaccination withgreater vigour, while making clear to the public theextent of the risks it still carries. At the same time weshould do all we can to reduce these risks; and in timeimprovement may appear.

Unhappily, successful primary vaccination does notensure continuing immunity: " The duration of

immunity conferred by vaccination against smallpox ininfancy is known to be of variable extent, and the

presence of a good vaccination scar does not mean that1. Ministry of Health: Memorandum on Vaccination against Smallpox.

H.M. Stationery Office, 1956.2. Report of the Ministry of Health, 1960. Part II: On the State of the

Public Health; p. 53. H.M. Stationery Office, 1961.3. See Lancet, Feb 24, 1962, p. 436.4. ibid. p. 439.

the person possessing it will not contract the disease." 5In the Middle East in the 1939-45 war, immunitycommonly lasted less than two years.6 No averagefigure can be relied on: many years ago STEVENSON,’director of the Government Lymph Establishment, drewattention to the fact " that the degree and the duration ofthe protection varies in individuals and that in exceptionalcases it falls very short of the average." In MadrasDOWNIE et al. have shown that of a group of adults,mostly aged 20-30, with good scars from infant vaccina-tion, about 10% had little or no neutralising antibody inthe serum. Thus periodic revaccination is essential-forchildren, the Ministry suggests,l on entry to and againon leaving school, and in adult life at intervals that

may be as short as three years for those at special risk.Where an outbreak does occur, protection of the non-immunised is aided by two factors. First, cases are

rarely infective in the prodromal stage; in MadrasDOWNIE et awl. isolated no virus from mouth washingsand garglings of patients in the first two days of illness.Secondly, vaccination of contacts is usually effective ifcarried out within three days after exposure, using apotent vaccine and proper technique; and here we mayrecall the Ministry of Health’s insistence 1 that, whenvaccinating or revaccinating in the face of possibleexposure to smallpox infection, the vaccine should beintroduced (either by the scratch method or by " mul-tiple pressure ") in two separate areas at least one inchapart. Another possible means of protecting contacts,in an outbreak, is to give them immune y-globulinfrom the sera of recently vaccinated adults 10; but theplace of this prophylactic is not yet entirely clear.World-wide eradication of smallpox is something to

which we can look forward confidently. But the diseasewill not be permanently eradicated, even from this

country, so long as the vaccination-rate remains as low asit is at present. Besides greater effort in this direction,there is still room, as the Madras studies show, for muchfurther research on methods both of prevention and oftreatment.

Thinking in NumbersMEDICAL statistics is by no means an exclusive

specialty, but has attracted hygienists, physicians,pathologists, and many others who find its methods

productive of new knowledge and (even more) of newquestions. Among them Prof. ROBERT CRUICKSHANKhas been both a practitioner (with his studies of infectionwithin the family) and a source of encouragement toothers; and as Lister fellow of the Royal College ofPhysicians of Edinburgh he has been able to display hisenthusiasm to a wider audience." The examples which5. Wld Hlth Org. Chron. 1962, 16, 13.6. Illingworth, R. S., Oliver, W. A. Lancet, 1944, ii, 681. Easton, J. H. L.

Publ. Hlth, Lond. 1945, 58, 110.7. Stevenson, W. D. H. Lancet, 1944, ii, 697.8. Downie, A. W., Hobday, T. L., St. Vincent, L., Kempe, C. H. Bull.

Wld Hlth Org. 1961, 25, 55.9. Downie, A. W., St. Vincent, L., Meiklejohn, G., Ratnakannan, N. R.,

Rao, A. R., Krishnan, G. N. V., Kempe, C. H. ibid. p. 49.10. Kempe, C. H., Bowles, C., Meiklejohn, G., Berg, T. O., St. Vin-

cent, L., Sundara Babu, B. V., Govindarajan, S., Ratnakannan, N. R.,Downie, A. W., Murthy, V. R. ibid. p. 41.

11. Measurements in Medicine. By ROBERT CRUICKSHANK. Royal College ofPhysicians of Edinburgh, 1961. Pp. 46.